Phase 2 - Microbio Flashcards
Define pathogen
Organism that causes or is capable of causing disease
Define commensal
Organism which colonises the host but causes no disease in normal circumstances - e.g. bacteria from throat can cause pneumonia in lungs
Define opportunist pathogen
Microbe that only causes disease if host defences are compromised
Define virulence/pathogenicity
The degree to which a given organism is pathogenic
Define asymptomatic carriage
When a pathogen is carried harmlessly at a tissue site where it causes no disease
Resolving power of naked eye
100μm
Resolving power of light microscope
0.2μm
Typical size of protazoa like entamoeba histolytica
~30μm
Common size of spirochetes like borrellia recurrentis
~15μm
Common size for bacilli like e. coli
~2-3μm
Common size of cocci
~1μm
Which is the biggest virus we learn of
Rotavirus
What is the typical size of viruses
All smaller than 1μmBigger viruses ~0.3-0.8μmSmaller virus <0.1μm
What is the smallest virus we learn of
poliovirus
What is unique about the nature of Chlamydia trachomatis
It is a bacteria but it is an obligate intracellular organism - it’s smaller than rotavirusRickettsia and Coxiella are also obligate intracellular bacteria
Define serovar/serotype
a distinct variation within a species of bacteria/viruses/among immune cells of different individuals
Which areas are open to bacterial colonisation
Mucosal surfacesBacteria can also get into many organs and cause inflammation
What do the colours of the gram stain signify
Purple - gram positivePink/red - gram negativepurPle - Positive; piNk - Negative
Basic shapes of bacteria
Coccus (round berry-like)diplococcus (2 cocci)streptococcus (chain of cocci)staphylococcus (cluster of cocci)Bacillus (rod)Chain of rodsVibrio (curved rod)Spirochete (spiral rod)Filamentous/branching bacteria
Typical structures that a bacterium is composed of
Chromosome of circular double ctranded DNA (free in cytoplasm)Inner membraneOuter membranePili/fimbriaeCell wallSome bacteria also have - a capsule made from polysaccheride- flagella- plasmids, which can be transferred from bacterium to bacterium
On which bacteria are capsules more common and why
On bacteria which get into blood/lungsIt helps protect them against the immune system
What is the purpose of pili/fimbriae
Recepting/sensing the environment
Which stain is commonly used for mycobacteria; what colour does it stain?
Ziehl-Neesen stain - stains red
How does the ziehl-neelsen stain only stain non-gram bacteria? What is the term used for this kind of bacteria?
There is a stage in the Ziehl-Neelsen stain where the bacteria are bathed in alcohol/acid. Regular gram bacteria are decolourised at this stage but certain organisms like mycobacteria resist the acid.These are called acid/alcohol fast bacteria (AFB or AAFB)
Describe the cell envelope of a gram positive bacterium
Thin cytoplasmic membraneThick layer of peptidoglycan with lipoteichoic acid strands within itPotentially a capsule
Describe from inside to out the cell envelope of a gram negative bacterium
Cytoplasmic membrane:- Thin inner membrane- Very thin layer of peptidoglycan- (piller-like) Lipoproteins within periplasmic space- Thin outermembraneLipopolysaccerides (ENDOTOXIN) - composed of:- Lipid A- O antigen- Terminal sugarspotentially a capsule
What is the peptidoglycan in bacteria
Crosslinked sugers and amino acids
What causes the difference in staining between gram positive and negative bacteria?
Gram positive bacteria are able to resist decolouration (usually a mix of ethanol and acetone) due to their thick peptidoglycan layersGram negative have a thin peptidoglycan layer so the stain is easily lost and they have to be counterstained (with safranin or basic fuchsin stain)
What is a spore
Small oval or spherical structures with thick walls which are very resistant to high temperatures, radiation, desiccation and chemical agents. They are involved in reproduction and are used by certain bacteria to defend themselves. They can last for a long time in the environment
What environment can bacteria survive in?
Temperature: <-800C to + 80CpH: <4 - 9Water/desiccation: 2 hours - 3 monthsLight: could be killed by UV
What environment can spores survive in
Temperature: <-800C to 1200C pH: <4-9Water/desiccation: >50 years
Growth rate of bacteria (give doubling time)
Common bacteria like E. coli or S. aureus:- In a broth or solid media: 20-30 minMycobacterium tuberculosis in broth or media:- 24 hoursMycobacterium leprae in broth or media:- 2 weeks
What is typically done now to test for mycobacteria in a culture
Grow too slowly for regular agar plate techniques ao using nucleic acid boosting techniques/PCR can be useful
Types of bacterial toxins
ENDOTOXINComponent of the outer membrane of GRAM NEGATIVE bacteria, eg lipopolysaccharidesEXOTOXINSecreted proteins of Gram positive and Gram negative bacteria
What is an example of a condition caused by bacterial exotoxins
Tetanus - causes simultaneous, prolonged, severe muscle contraction
Differences between Endo- and Exotoxins (bacterial)
Exotoxins are composed of protein, endotoxins are composed of lipopolysacherride.Exotoxins have specific action while endotoxins are non-specificexotoxins are labile in heat, endotoxins remain stableexotoxins have strong antigenicity, endotoxins have weak antigenicityexotoxins are produced by both gram positive and gram negative; endotoxins are only found on gram negative (LPS)exotoxins can be converted to toxoid; endotoxins cannot
How many chromosomes do bacteria normally contain
1typically 2-4 x10^3 kb (kilobase - 1kb= 1000 bases)
How many RNA polymerases do bacteria have
1
What type of ribosomes do bacteria contain
30s/50s
What does much of bacterial antibiotic resistance result from
Point mutations. Commonly:- base substitution- deletion- insertion
How many bases typically in a plasmid
10-60 kb
Name some sections commonly found in a plasmid
- Transfer promotion genes- plasmid maintenance genes- antibiotic/virulence determinant genes
How are plasmids typically transferred between bacteria
Bacterial conjugation
How can gene transfer occur in bacteria
- Transformation (gain from environment) eg via plasmid- Transduction eg via bacteriophage- Conjugation eg via sex pilus
Where does most bacterial variation come from
Gene transfer - lateral transfer of genes
Name the main obligate intracellular bacteria
Genus Rickettsia:- R. rickettsii - R. prowazekii- R. conorii- etc.Genus Chlamydia:- C. trachomatis- C. psittaci- C. pneumoniaeGenus Coxiella:- C. burnetii
Which notable illness is caused by the Rickettsia genus of bacteria
Rickettsia rickettsii causes:- scrub typhus/rocky mountain spotted fever- transferred via tick
Which notable illnesses are caused by the Chlamydia genus
Chlamydia trachomatis can cause:- the STI- trachoma (eye infection)Chlamydia psittaci causes:- bird related pneumonia (can get from kissing pet parrots)Chlamydia pneumoniae:- associated with respiratory tract infections
Name the bacteria that may be cultured on artificial media AND has NO cell wall
Mollicutes:- Mycoplasma pneumoniae (atypical pneumonia)- M. hominis (STIs and infertility)- Ureaplasma urealyticum
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as filaments
Genus ACTINOMYCES e.g. A. israeliiGenus NOCARDIA e.g. N. asteroidesGenus STREPTOMYCES (important source of antibiotics)
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as single cells AND are cocci AND gram negative
Anaerobic: Genus VEILLONELLAAerobic: Genus NEISSERIA- N. meningitidis- N. gonorrhoeae
What diseases are caused by the genus Neisseria
N. meningitidis causes:- meningitis in late teens/early twentiesN. gonorrhoeae causes:- gonorrhoea (2nd most common bacterial STI)- has increased bacterial resistance
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as single cells AND are cocci AND gram positive
Anaerobic:- PEPTSTREPTOCOCCUS- ENTEROCOCCUS (E. faecalis)Aerobic:- STAPHYLOCOCCUS- STREPTOCOCCUS
How can Staphylococcus be further divided up
Coagulase positive:- S. aureus(- S. intermedius)Coagulase negative:- S. epidermidis(- all other staph species)
How can Streptococcus be further divided up
Alpha-haemolytic:- Viridans streptococcus- S. pneumoniae- S. sanguis- S. oralisetc.Beta-haemolytic:- S. pyogenes- S. agalactiaeetc.Non-haemolytic:- S. bovis
What do different haemolytic reactions look like
Alpha-haemolytic partially lyses blood (via production of hydrogen peroxide) so makes the bacterial colonies look greenBeta-haemolytic fully lyses haem (via production of 2 pore-forming toxins) so turns blood agar clearNon-haemolytic can’t lyse blood (also known as gamma-haemolysis)
What is the Lancefield classification? Give names of relevent bacteria.
It classifies bacteria from group A to group G based on which antibody they have - S. pyogenes is Lancfield group A- S. agalactiae is Lancefield group B- Enterococcus faecalis (a different genus, NOT a strep) is Lancefield group D
Diseases caused by staph
S. aureus - associated with skin infections; also sometimes endocarditis, particularly after dental surgeryS. epidermis is oppertunistic, normally lives on skin but can cause infection if the human is compromised (e.g. due to catheter, plasters etc.)
What diseases are caused by strep
S.pyogenes:- associated with pus, - causes scarlet fever- strep throatS. pneumonia causes:- common pneumonia- meningitis in older peopleAlpha-haemolytic strep - esp. viridans- associated with infective endocarditis
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND acid fast
MYCOBACTERIA:- M. tuberculosis (TB)- M. leprae (leprosy)- M. avium-intracellulare- M. ulcerans- M. kansasii- etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram positive
Anaerobic:- CLOSTRIDIUM* C. tetani (tetanus)* C. difficile (diarrhea)* C.perfringens* C. botulinumetc.- PROPIONIBACTERIUM* P. acnesAerobic:- CORYNEBACTERIUM* C. diphtheriaeetc- LISTERIA * L. monocytogenesetc- BACILLUSB. anthracis (Anthrax)B. cereus (food poisoning)etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative
Anaerobic:- BACTEROIDES* B. fragilisAerobic:- ‘Coliforms’ (gut bacteria - non-spore forming)- ‘Pseudomonads’ (belonging to pseudomonas genus)- ‘Vibrio’ (curved rod)- ‘Parvobacteria’ (small, fastidious, non-spore forming coccobacilli)
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are coliforms
ESCHERICHIA- e.g. E. coli KLEBSIELLA SALMONELLA - e.g. S. typhi SHIGELLA - e.g. S. sonnei CITROBACTER PROTEUS YERSINIA- e.g. Yersinia pestis etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are Pseudomonads
PSEUDOMONAS- e.g. P. aeruginosa
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are vibrio bacteria
VIBRIO- e.g. V. choleraeCAMPYLOBACTER- e.g. C. jejuniHELICOBACTER
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are parvobacteria
HAEMOPHILUS- eg H. influenzae BRUCELLABORDETELLA- e.g. B. pertusissPASTEURELLA
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are spirochaetes
LEPTOSPIRA- e.g. L. icterohaemorrhagiae (Leptospirosis)TREPONEMA- e.g. T. pallidum (syphilis)BORRELIA- B. burghdorferi (lyme disease)- B. recurrentisetc
Which antigenic groups of strep are Beta-haemolytic?
A, B, C, G
How do you differentiate between viridans strep and S. pneumoniae?
Optochin test- Viridans strep is resistant to optochin; S. pneumonia is sensitive to optochin- On agar culture - optochin sensitivity looks like an area around the optochin disk that is clear of bacteria
How do you differentiate between S. aureus and other staphylococcus
Coagulase/DNAse test- S. aureus is coagulase positive (also s. intermedius)- rest are negative
What is a go-to antibiotic for staph infections
Flucloxacillin
How many species of staph are there
at least 40
What is coagulase? Why might this be produced?
Enzyme produced by bacteria that clots blood plasma- Fibrin clot formation around bacteria may protect from phagocytosis
Where is the normal habitat of staph
nose and skin
Are coagulase +ve or -ve staph more likely to cause problems
Coagulase +veCoagulase -ve species (e.g. S. epidermidis) only important as opportunistic infections
How is staph aureus spread
Aerosol and touch- some people are carriers/shedders
What are S. aureus’ virulence factors
Pore-forming toxins (in some strains)- α - haemolysin (low levels: apoptosis, high levels: mass necrosis)- Panton-Valentine Leucocidin ‘PVL’ (causes hemorrhagic pneumonia)Proteases - Exfoliatin (exotoxin - scalded skin syndrome)Toxic Shock Syndrome toxin (super antigen)- (stimulates cytokine release)Protein A - (surface protein which binds antibodies in wrong orientation)
What is MRSA?
Methicillin (aka flucloxacillin) Resistant S. aureus- resistant to major antibiotics- break open beta-lactam ring of certain antibiotics- resitant to gentamicin, erythromycitetracycline
Types of S. aureus infections
Pyogenic:- wound infections- causes:* abscesses* Impetigo* Septicaemia* Osteomyelitis* Pneumonia* EndocarditisToxin mediated:- Scalded skin syndrome- Toxic shock syndrome- Food poisoning
Name the main coagulase -ve staph species
- S. epiderimidis- S. saprophyticus
Characteristics of S. epidermidis
- Oppertunistic infections* common in immunocompromised and people with prostheses- Main virulence factor - ability to form persistant biofilms (clusters of bacteria that are attached to a surface and/or to each other and embedded in a self-produced matrix)
Characterictisics of S. saprophyticus
Causes acute cystitis (UTI)- commonly comes from skin contact in sexual intercourseVirulence factors:- haemagglutinin for adhesion- urease
Is S. pyogenes aerobic or anaerobic?
It’s facultatively anaerobic (can grow anaerobically or aerobically)
Is S. pyogenes penicillic sensitive?
Yes
Where is s. pyogenes most likely to infect?
Throat, skin, post partum infections
What kind of infections are s. agalactiae associated with
Neonatal infections - passed from mother to child
How are Lancefield groups tested? Describe the procedure.
Lancefield microbead agglutination test:- Antiserum (solution of antibodies) made that recognise each specific group- The antiserum is tagged to tiny plastic beads- These are added to a suspension of bacteria- If the bacterial antigen is complementary to the antiserum, they bind together and cause the beads to clump together- this is visible to the naked eye
Virulence factors of S. pyogenes
Exported factors:- Enzymes* Streptokinase (important) ** breaks down clots * Hyaluronidase ** spreading * C5a peptidase ** reduces chemotaxis- Toxins* Streptolysins O&S (Important) ** binds cholesterol* Erythrogenic toxin (Importnat) ** Streptococcal pyrogenic toxin e.g. SPeA – exaggerated response ** Can lead to scarlet fever in childrenSurface factors:- Capsule - hyaluronic acid - M protein – surface protein (Important) (encourages complement degradation) * can cause scarlet fever in children
Infections caused by S. pyogenes
Respiratory- Tonsillitis & pharyngitis (most common)- Otitis mediaSkin and Soft tissue- Wound infections- Impetigo- cellulitis - puerperal feverScarlet fever- SPeA and M typeComplications- rheumatic fever- glomerulonephritis
Characteristic appearances of S. pneumonia in culture/tests
- “draughtsman” colonies (depressed central part with raised edges)- α- haemolytic- Gram positive cocci in pairs- Optochin sensitive
Where is S. pneumonia often found (non-pathogenically)
Found as a commensal in oro-pharynx of 30% of population
What does S. pneumoniae cause pathogenically
PneumoniaOtitis medis (middle ear infection)SinusitisMeningitis
What factors predispose to S. pneumoniae infection
- Impaired mucus trapping (e.g. viral infection)- Hypogammaglobulinaemia (problems making antibodies)- Asplenia (absence of spleen)- HIV
S. pneumonia virulence factors
Capsule- polysaccharide (84 types), antiphagocytic Inflammatory wall constituents- teichoic acid (choline)- peptidoglycanCytotoxin- pneumolysin (pore-forming)
Which vaccines are there for S. pneumoniae infection
- polysaccharide vaccine ‘PPV’ - contains 23 types of pollysaccheride antigens from s. pneumoniae capsule- conjugate vaccine ‘PCV’ - contains 13 types of pollysaccheride antigens from s. pneumoniae capsule
Who are S. pneumoniae vaccines given to and why
Only at risk people over 2 y/oThe immune response to polysaccheride antigens is poor in the very young
Who is at risk for S. pneumoniae infection
People with:- sickle cell disease, - asplenia, - renal disease, - immunodeficiency, - diabetes - chronic liver disease
How does pneumolysin form pore
Subunits assemble into a ring structure on host cell surface thus forming a pore in the membrane
Characteristics of Viridans group strep
α- haemolytic (or non-haemolytic)Optochin resistant
What diseases can Viridans group strp cause
- Some cause dental caries & abscesses - typically live in mouth- Important in infective endocarditits (difficult to diagnose and treat)- Cause deep organ abscesses (e.g. brain, liver)
Which strep species are typically associated with infective endocarditis? What is a typically presentation of this?
- S. sanguinis- S. oralisVery typical for people to get endocarditis after having dental surgery - they get into the blood from the mouth
Most virulent group of Viridans group strep
‘milleri group’S.intermedius, S.anginosus, S.constellatus
Main aerobic Gram positive bacilli
- Listeria monocytogenes - Bacillus anthracis- Corunebacterium diphtheriae
What does listeria monocytogenes cause?
causes listeriosis (starts as type of food poisoning - grows in moist areas)- usually self-limiting- can cause issues in immunocompromised people and pregnant women
What does bacillus anthracis cause?
Anthrax- associated with cattle- spore forming so can be around for a long time3 syndromes depending on route of acquisition:- Cutaneous - blister with black centre (‘eschar’)- Inhalation - respiratory sepsis- Ingestion - severe gasteroenteritis
What does corynebacterium diphtheria cause
Diphtheria- infectin of pharynx* thick greyish pseudo membrane on tonsils can be a characteristic of it- involves infection of immune cells- involves metachromatic granules
Main anaerobic gram positive bacilli
All main are types of CLOSTRIDIA- C. tetani- C. botulinum- C. difficile
What does C. tetani cause? Associated symptoms and characteristics.
Tetanus- muscle contractions and stiffness progressing from head to body (neck stiffness, sore throat, difficulty opening mouth) - rictus grin- Get from infected wounds- Toxin inhibits GABA
What does C. botulinum cause?
Botulism- paralysis spreading from head to body (from Botulinum toxin)- from contaminated food or infected wounds
What does C. difficile cause?
Antibiotic associated diarrhea (as it kills off good bacteria and leaves C. difficile able to colonise more of the gut)- pseudomembranous colitis (destroys coloon)
What are the components of LPS
- Lipid A - the toxic portion that is anchored in the outer leaflet of outer membrane- Core (C) antigen (AKA core oligosaccheride) - short chain of sugars, some are unique to LPS- Somatic (O) antigen (O-polysaccheride) - highly antigenic repeating chain of oligosaccherides
Why do mycobacteria or mycoplasmas not stain with Gram stain? Are they considered gram positive or negative?
Mycobacteria outer lipid bilayer is composed of Mycolic acidsMycoplasmas don’t have peptidoglycan- They are phylogenetically considered Gram positive
The two types of virulence factors/pathogenicity determinants
Colonisation factorsToxins (‘effectors’)
Name colonisation factors
Adhesins, invasins, nutrient acquisition, defence against the host
What are toxins/’effectors’ released by gram bacteria?
- Usually secreted proteins that cause damage and subversion- In gram neg bacteria the protein secretion system spans both layers on the cell membrane - proteins are translocated from inside cytoplasm and secreted
Which bacteria are within the Phylum proteobacteria
Enterobacteriaceae or Enterobacteria FAMILY (contains Shigella, salmonella, escherichia etc.)Vibrio (e.g. vibrio cholerae)PseudomonansHaemophilus (e.g. H influenza)Legionella (e.g. Legionella pneumophila)Bordetella (e.g. bordetella pertussis)NeisseriaCampylobacterHelicobacter (e.g. Helicobacter pylori)
Characteristics of Enterobacteria
RodsMost are motile (have peritrichous flagella - flagella over their entire surface, like around the perimeter)Some species colonise the gut (commensals and pathogenic)Facultatively anaerobic
Name main members of enterobacteria?
ShigellaEscherichia (esp E. coli)Salmonella (e.g. S. enterica)Proteus (e.g. P. mirabilis)Klebsiella (e.g. K. pneumoniae)Less relevent according to lecturer:Serratia (e.g. S. marcenescens)Yersinia pestisEnterobacter spp.
Which main enterobacteria are lactose use positive?
E. coliKlebsiella pneumoniae
Which main enterobacteria are motile
E. coliSalmonella entericaSerratia marcensens (is this important??)Yersinia pestis at 25 degrees C (NOT motile at 37 degrees so NON-MOTILE inside humans)Proteus mirabilis
Which main enterobacteria are NOT motile?
Shigella flexneriKlebsiella pneumoniaeYersinia pestis at 37 degrees C
How do you test Lactose phenotype?
On MacConkey agarSelective for gram-negative bacteria (contains bile salts and crystal violet)Contains indicator so Lactose metabolising positive organism colonies turn red
Which antigen is associated with flagella
H antigen
How do you discriminate between similar bacteria like Salmonella and Shigella
Serology(in this case, no H (flagella) antigen pressent for Shigella)
What is serotyping
Differentiating between specieses/strains by identifying cell surface antigens
What is a serovar
Antigenically distinct varients of a single species
What are the 3 main antigenic determinants for serotyping in gram negative bacteria
K antigen (exopolysaccheride ‘capsulel’)H antigen (flagella)O (somatic) antigen (LPS)
What is Escherichia coli normally
Commensal gram -ve bacteria - most abundant facultative anaerobe in gut (10^7-10^8/g faeces)Has peritrichous flagella
Principal infections caused by pathogenic E. coli
(i) Wound infections (typically post-surgical)(ii) UTIs (cystitis; 75-80% of female UTIs - faecal source or sexual activity; * catheterisation - most common type of nosocomial (originating in hospital) infection)(iii) Gastroenteritis(iv) Travellers’ diarrhoea(v) Bacteraemia (can be asymptomatic - sometimes leading to sepsis syndrome)(vi) Meningitis (infants) - rare in UK
What are the species’ of Shigella
S. dysenteriae, S. flexneri, S. boydii, S. sonnei
What does shigella cause
Shigellosis: severe bloody diarrhoea (bacillary dysentery)- S. dysenteriae causes most severe form.BUT - S. sonnei most prevalent in developed world.
Where is Shigella infection often found
Endemic in developing countries where sanitation is poor – mainly in children.
Symptoms of shigellosis
Frequent passage of stools (>30/day)Small volume, pus and blood, prostrating cramps, pain in straining, feverUsually self-limiting (in adults)
Pathogenesis of Shigella infection
Acid-tolerant (low infective dose, ~10^2)Person-to-person, or contaminated water & food(fresh/raw vegetables used in salads)Entry through colonic M cells (antigen sampling cells - lie over lymphoid follicles and deliver antigens to underlying immune cells)Induced uptakeImportant virulaence factor: Shiga toxin
Pathology of Shigella
- lands on M cell apical surface- gets taken to basolateral surface- phagocytosed by macrophage (but rmains unharmed)- Shigella induces apoptosis of macrophage- moves laterally, destroying tissue- Macrophages also release cytokines to attract polymorphoneuclear leukocytes to the site of in fection causing more tissue damage
What are the 2 specieces of Salmonella
S. enterica (has >2 500 serovars, including Salmonella enterica serovar Typhi)S. bongori (rare - contact with reptiles)
What does S. enterica cause
salmonellosis (usually from contaminated food/drink)3 forms:1. Gastroenteritis/enterocolitis2. Enteric fever3. Bacteraemia (bacteria in blood)
Pathogenesis of salmonellosis
Ingestion of contaminated food/water - high I.D. (infective dose)(~10^6) (‘faecal-oral route’)→ Invasion of gut epithelium (small intestine)→ Transcytosed to basolateral membrane→ Enters submucosal macrophages→ Intracellular survival/replicationIn Serovars Enteritidis and Typhimurium:- intestinal secretion and inflammatoryresponse are LOCALISED- DO NOT produce toxinsIn serovar Typhi:- Infection is SYSTEMIC due to dissemination within macrophages (macrophages migrate to reticuloendothelial organs via lymph and blood)- produces TYPHOID TOXIN (has DNAse activity - a genotoxin)
Gastroenteritis/enterocolitis - causes and characteristics
Caused by serovars Enteritidis and TyphimuriumFrequent cause of food poisoning (milk, poultry meat & eggs)Second highest no. of food-related hospitalisations/deaths (UK)6-36 hr incubation period, resolves (~7 days) Localised infection, only occasionally systemic
Enteric fever - causes/characteristics
Typhoid/paratyphoid fever - caused by serovars Typhi and ParatyphiLinked to poor quality drinking water/poor sanitation Systemic disease ~20 million cases, ~200,000 deaths/year (globally)
What causes Bacteraemia
Serovars Cholerasuis and Dublin- it is uncommon
Steps of gastroenteritis pathogenesis
- Bacterial-mediated endocytosis 2. Induction of interleukin-8 release →3. Neutrophil recruitment and migration4. Neutrophil-induced tissue injury →5. Fluid and electrolyte loss → diarrhoeaInflammation/necrosis of gut mucosa
Steps of enteric/typhoid fever pathogenesis
- Bacterial-mediated endocytosis2. Transcytosis to basolateral membrane3. Survival in macrophage (MΦ) → systemic spread Initially, little damage to gut mucosa
What % of people become carriers of S. enterica serovar Typhi
~10% are carriers for < or = 3 months (bacteria shed in faeces)~ 1-4% become chronic carriers (at least a year or more)
Notable characteristic of Proteus mirabilis
Can differentiate into an elongated hyperflagellated form → gives it surface motility (ability of ‘swarming’) over solid surface
What does Proteus mirabilis cause
Catheter-associated UTIs (~30% of cases)- can ascend and cause pyelonephritis (kidney infection)Formation of bladder/kidney stones, can block catheter- does this by producing urease (increasing urine pH) which forms ammonia and leads to calcium phosphate precipitation
Characteristics of Klebsiella pneumoniae
- environmental (it is an enterobacteria but more common in environment)- opportunistic, nosocomial infections (neonates, elderly, compromised)- colonisation of gastrointestinal tract (normal) and oropharynx (less frequently) is often benignMulti-drug resistant (resistant to carbapenems)
What does Klebsiella pneumoniae cause
UTI, pneumonia (aspiration from oropharynx), surgical wound infections from gut, bacteraemia → sepsis (high mortality).
Characteristics of Vibrio cholerae
- Facultative anaerobe- Normally from Saline environments: commensal to planktonic crustaceans such as copepods → ingestion by shellfish → contamination of drinking water due to flooding of coastal areas or poor sanitation (faecal contamination)- characteristic curved rod shape
What does vibrio cholerae cause
Cholera: Most severe diarrhoeal diseaseAssociated with LPS O1 serotype → epidemics (and occasionally O139 variant)Characterised by pandemics (7 recorded since 1817)
History of Choleral pandemics
1P-6P, Indian subcontinent;7P began in Sulawesi (1961) → SE Asia (1963) → Africa (1970) → Latin America (1991) → Caribbean (2010)1.4-4.0 million cases/year, 20,000-140,000 associated deaths
General pathology of Cholera (aquisition, incubation, consequence)
Faecal-oral route (not person-to-person) - high infective dose required (not acid resistant)(faecal contaminated water (poor sanitation) or undercooked shellfish from risk areas) ↓Incubation, few hours to 5 days (V.c. multiplies in small intestine) ↓Voluminous watery stools (‘secretory’ diarrhoea - rice water stool)Can lose 20 litres fluid/day plus electrolytes → dehydration/death (hypovolaemic shock) → 50-60% mortality if untreatedNo blood, pus or fever (i.e. not dysenteric)i.e. no invasion or damage to mucosa
What can most cases of Cholera be treated by
Oral re-hydration therapy (ORT)
What is the main virulence factor of V. cholerae
Cholera toxin
Pathogenesis of Cholera (mechanism of cholera toxin)
CT binds to a glycolipid receptor on epithelial cell (B subunits)A subunit ADP-ribosylates G-protein (Gs) → locked in ‘ON’ stateUncontrolled cAMP productionProtein kinase A activatedPhosphorylates CFTR (cystic fibrosis transmembrane conductance regulator) anion transporterCFTR activity modified (loss of Cl- & Na+ into gut lumen) → massive loss of H2O
Characteristics of Pseudomonas aeruginosa
Ubiquitous, free-living (in environment), motile (single polar flagellum), rod-shaped.Opportunistic (serious cause of nosocomial infections)Resistant to multiple antibiotics (& disinfectants) - very difficult to treat
Infections caused by P. aeruginosa. Can it cause acute or chronic?
Acute infections:(i) Localised - burn/surgical wounds - UTI (catheters) - Keratitis (infection of cornea - requires some kind of scratch etc.)(ii) Systemic (bacteraemic → sepsis - hard to treat) - affects neutropenic patients - low white blood cell count (leukaemia, chemotherapy, AIDS)(iii) affects ICU patients (ventilator acquired pneumonia) - leading cause of nosocomial pneumoniaChronic infections:(i) In Cystic fibrosis (CF) patientsCommon denominator to all infections - compromised host defences
What happens in cystic fibrosis (general overview)
Defective CFTR (chloride ion transporter)→ thick mucus produced in lungs.- Lungs prone to microbial infection
Most problematic source of infection for CF patients
P. aeruginosa
Types of P. aeruginosa
P. aeruginosa ‘wild-type’ (non-mucoid)P. aeruginosa ‘CF’ phenotype (mucoid) = mutants that secrete a thick coating of exopolysaccharide (i.e. hyper-produce capsule): provides additional protection against host defences in the lung
What leads to the progressive lung damage following infection of CF lung by P. aeruginosa
Mainly due to effect of host immune system trying to clear infection
Characteristics of Haemophilius influenzae
Exclusively human parasite (obligate/ no environmental reservoir):Nasopharyngeal carriage in 25-80% population (non-capsulate strains)- transient carriage of capsulate strains occurs in 5-10% (more dangerous as they are invasive - can move around body)Oppertunistic
Who are particularly susceptible to H. influenzae infection
Young children and adult smokers
What infections can Haemofilius influenza cause
- Meningitis* (age <5 yrs), 5-10% of adult cases ∙ Bronchopneumonia ∙ Epiglottitis, sinusitis, otitis media ∙ Bacteraemia (often associated with pharyngitis) ∙ Pneumonia in CF, COPD, HIV patients* infections caused by capsulate strains (invasive) – uncommon in healthy adults
Diagnostic characteristics of H. influenxae
Fastidious - requires ‘factor X’ (haem) and ‘factor Y’ (NAD) - requires chocolate agar (lysed/oxidised blood)Non-motile
Virulence determinants of H. influenzae
(i) Capsule - invasive strains are capsulate (‘encapsulated’) → can penetrate nasopharyngeal epithelium → resistance to phagocytosis and complement system - 6 different capsule serotypes (a-f) (type b strains are the main cause of meningitis)Commensals and upper respiratory tract pathogens are non-capsulate referred to as ‘non-typeable’ H. influenzae (NTHi)(ii) LPS (‘endotoxin’) → inflammation → complement resistance
Which vaccine has reduced the cause of H. influenza caused meningitis
Hib vaccine (HH. influenza type b)
What does Legionella pneumophila cause, source of acquisition and who does it usually affect
Legionnaires’ disease - severe inflammatory pneumonia (1-3% of all pneumonias) - 15-20% mortalityInfection from man-made aquatic environments (air-conditioning cooling towers, shower heads, nebulisers, humidifiers etc.) - never person-to-person transmission - replicate within freshwater protozoa- can repliacte in alveolar macrophages tooAffects immunocompromised (elderly, alcoholics, smokers etc.)
What does Bordetella pertussis cause
Pertussis (whooping cough)Non-specific flu-like symptoms (~7 d), followed by paroxysmal coughing(https://www.youtube.com/watch?v=l5SHtdczSBc)(B. parapertussis causes mild pharyngitis)
Characteristics of B. pertussis
Humans - only known reservoir (obligate human pathogen)Highly contagious (low I.D.) - aerosol transmission(- produces pertussis toxin and Adenylate cyclase-haemolysin toxin (CyaA))Non-invasive
Diagnostic characteristics of B. pertussis
Short (sometimes oval) rods (coccobacilli)FastidiousGram negative
Diagnostic characteristics of Neisseria
Non-flagellated diploccociFastidiousGram -ve
Where can Nessieria be found in the environment
Humans are the only known reservoir
Characteristics of N. meningitidis
Nasopharyngeal carriage in 5-10% population (asymptomatic) Rises to 20-90% during outbreaksPerson-to-person (aerosol) transmission (universities, barracks, Haj)
Pathogenesis of N. meningitidis
crosses nasopharyngeal epithelium and enters bloodstream → low level - bacteraemia (asymptomatic) or high level - septicaemia (sepsis - high mortality if not treated) → meningitis: invasion of the meninges - bacteria enter CSF of subarachnoid space after crossing blood-brain barrier(second most frequent cause of meningitis in young children)
Virulence determinants of N. meningitidis
(i) Capsule is major virulence determinant (serogroup B - 90% cases) → anti-phagocytic(noncapsulated N.m. only found in nasopharynx - not pathogenic)(ii) LPS (membrane ‘blebs’) → cytokine cascade → sepsis
What are non-blanching petechial pr purpuric rashes associated with
Meningococcal sepsis(capillary damage - bleeding - ecchymosis AKA bruising)
What does N. gonorrhoeae cause
Gonorrhoea - second most common STD worldwide
How is gonorrhoea transmitted
Person-to-person only
How often can N. gonorrhoeae infection be asymptomatic
~10% men, ~50% women
Characteristic infection presentation of gonorrhoea
Urethritis with additional infection of female genitalia. Serious complications in women - can lead to salpingitis (fallopian tubes) and/or PID (pelvic organs) if infection ascends.Proctitis, gingivitis, pharyngitis depending on sexual preferenceCan transmit as conjunctivits to newborns
Are gonococci capsulated or not
They are non-capsulated
Helicobacter pylori appearance
spiral shape, tuft of polar flagella
Where are H. pylori found in the body
Discovered in gastric mucus (1982) which was previously thought to be sterile
Incidence of H. pylori in global population
Present in ~50% global population, but onlya fraction develop disease
Which diseases are H. pylori associated
Major role in gastritis and peptic ulcer disease (80-90% of ulcers)Implicated in ~10% cases of gastric adenocarcinoma & mucosa-associated lymphoid tissue lymphoma (linked to production of VacA and CagA toxins)
Name of main bacteria in Phylum bacteroidetes
Bacteroides
Characteristics of Bacteroides
Non-motile rodsObligate anaerobesCommensal flora of colon (most abundant organism in gut - 30-40% of total)Opportunistic
What amount per g of faeces is Bacteroides? Population ratio compared to E. coli?
> 10^10/g faeces (outnumbers E. coli 20:1)
What infections can infections can Bacteroides cause
Infection of tissue injury (surgery, perforated appendix or ulcer) → predominantly peritoneal cavity infections (peritonitis, intrabdominal abscesses are most common) can lead to bacteraemiaMost frequent cause of banaerobic infectionsOften present in polymicrobial infections with enterobacteria - presence of facultative anaerobes depletes O2, allowing anaerobes such as Bacteroides to proliferate
Which Bacteroides species is most commonly responsible for infections
B. fragilis(although it is only 0.5-1.0% of total commensal Bacteroides)
Which genuses are in Phylum Chlamydiae
Chlamydia and Chlamydophila
Characteristics of Chlamydia and Chlamydophila
Very small, non-motile.Obligate intracellular parasites.Many species within this group live asymptomatically as endosymbionts in amoebae, invertebrates and vertebrates.Cannot culture in bacteriological media - detect by serum Abs (antibodies - tho these could be due to previous infection so anleternate confirmatory test must also be done) or PCR (AKA NAA or NAAT)
Life cycle of Chlamydia and Chlamydophila
2 developmental stages:(i) Elementary bodies (EBs) - rigid, extracellular form, ~0.3 μm, dormant infectious enter cell through endocytosis prevent phagosome-lysosome fusion ↓ differentiates into…(ii) Reticulate bodies (RBs) - fragile, intracellular form, ~1.0 μm, metabolically active replicative non-infectious acquire nutrients from host cell
How many developmental stages in life cycle of Chlamydia/Chlamydophila
2- Elementary body stage- Reticulate body stage
Form/characteristics of Chlamydia/Chlamydophila Elementary bodies
Rigid, dormant extracellular form~0.3 micrometers
What occurs during the elementary body phase of Chlamydia/Chlamydophila life cyle
InfectiousEnter cell throughendocytosisprevent phagosome-lysosome fusion (so it can’t be destroyed by host defence of cell)
What happens in reticulate body phase of Chlamydia/Chlamydophila life cycle
Non-infectiousReplicationAcquire nutrients from host cell
Characteristic of Chlamydia/CHlamydophila reticulate body
fragile, metabolically active, intracellular formpleiomorphic~1.0 micrometers
Medically important members of genus Chlamydia
C. trachomatis (has 3 biovars):- trachoma biovar (serotypes A-C)- gentital tract biovar (serotypes D-K)- lympho granuloma venereum (LGV) biovar
What disease does the Chlamydia trachomatis biovar trachoma cause
Trachoma → blindness (eye-to-eye transmission via hands, fomites (innanimate objects like mascara brushes) or flies)Largest cause of preventable blindness caused by infectius organismsEasily treated if caught early but often not recognised till later
What does C. trachomatis biovar genital tract cause
Chlamydia STI- most common STD in UK - infects epithelial cells of mucous membranes of urethra (both sexes) and vagina- can ascend to uterus and ovaries (PID, infertility)- usually asymptomatic (i.e. 70-80% cases in women)Conjunctivitis (hand-to-eye transmission OR mother-to-child during delivery)
What does the lympho granuloma venereum (LGV) biovar of Chlamydia trachomatis cause
LGV (an STD) - invasive urogenital/anorectal infection- endemic to the tropics, cases rising in Europe/North America
Medically important members of Chlamydophila
C. pneumoniaeC. psittaci
What does C. pneumoniae cause
Resp tract infection (mild/’walking’ pneumonia)Causes ~10% community acquired pneumonias
What does C. psittaci cause
Psittacosis (severe pneumonia)Mainly affects bird owners (zoonotic)Uncommon
Spirochaete physical form
Long, slender, helical, highly flexible
Characteristics of Spirochaetes
Most are free-living and non-pathogenicPathogenic varieties difficult to cultureHas a modified outer membrane (Treponema and Borrelia lack LPS, have a different glycolipid instead)
Where is the spirochaete endoflagella located
Between peptidoglycan and outer membranePeriplasmic flagellaFixed at each end of bacterium and confers shapeOverlap in centre of bacterium
Characteristics of spirochaete endoflagella function
Propels in corkscrew motionSwims faster in high viscosity medium (i.e. normal environment of spirochaetes)‘Hides’ antigenic flagellum
What are the 3 medically important members of Spirochaetes
Borrelia burgdorferiLeptospira interrogansTreponema pallidum
What does Borrelia burgdorferi cause
Lyme disease
How is Lyme disease transmitted
Via ticksB.b. infects small mammels (e.g. rodents)Tick larvae feeding on the infected animal acquire B.b.Usually transmitted to humans by tick nymphs (adults easier to spot)
Symptoms of Lyme disease
Bull’s eye rashFlu-like symptoms (fever, fatigue, headache)(neurological problems in 10-15% patients, joints → arthritis)Most symptoms arise as consequence of immune response
How can lyme disease spread within the human body
dissemination via lymphatics/blood to other organs
What does leptospira interrogans cause
Leptospirosis (zoonosis) - rare in UKSymptoms of leptospirosis:- Flu-like- Severe form (Weil’s disease) in 10-15% infected individuals * jaundice, acute renal and hepatic failure, pulmonary distress, haemorrhage
How is leptospirosis acquired?
Contact of infected animal urine with mucous membrane or abraded skin
What does treponema pallidum cause
Syphilis
How many stages of syphilis (treponema pallidum infection)
3Primary stageSecondary stageTertiary stage
What occurs in primary stage syphilis (treponema pallidum infection)
Localised genital infection (chancre)Defined as days-weeks post-infection (i.e it is in the primary stage if it is occuring within days/weeks of being infected)
What occurs in secondary stage syphilis (treponema pallidum infection)
Systemicskin (rash), swollen lymph nodes, joint pains, muscle aches, headache, feverOccurs at 1-3 months post-infectionHighly transmissible~50% of cases are at secondary stage
What occurs in tertiary stage syphilis (treponema pallidum infection)
‘Gummas’ (granulomas) in bone and soft tissueCardiovascular syphilis (affects aorta)Neurosyphilis (affects brain and spinal cord)Occurs several years post-infectionNon-infectious
How can syphilis be treated
All stages can be treated with antibiotics but treatment is longer for tertiary stage syphilis and tertiary-related damage can’t be reverted
Name mycobacteria of medical importance and their relevant medical condition
M. tuberculosis - tuberculosisM. leprae - LeprosyM. avium complex (MAC) - Disseminated infection in AIDS, chronic lung infection (oppertunistic - doesn’t usually affect humans)M. kansasii - Chronic lung infection (oppertunistic - doesn’t usually affect humans)M. ulcerans - Buruli ulcer (west africa/ australia - often affects kids - doesn’t usually kill but maims)Rapidly growing mycobacteria (AKA M. fortuitum complex) - Skin/soft tissue infectionsM. marinum - fish tank granuloma (asymptomatic in tropical fish - skin conditions in humans)
Are most mycobacteria environmental or human organisms
Most are environmentalTB evolved to infect humans and some other mammals like bovines
How is leprosy (m. leprae) communicated
Through respiratory mediums Only infectious in early respiratory period
What effect does leprosy have on humans
Skin hypopigmentation - some lesions presentNeural lesion - loss of sensation and pain response
What socioeconomic factor is leprosy associated with
poverty
Stages of Buruli ulcer (m. ulcerans infection)
NoduleSmall ulcerLarge ulcerBone destruction (causes deformation)
What is severe Buruli ulcer associated with
Poverty - don’t have resources to seek medical help until sever, late stagesIt is treatable if found at an early stage
Characteristics of TB
Infects people over a long period of timePeople put large amount of bodies resources into fighting off TB thus causing consumptive appearanceLeading cause of death by infectious disease
Mycobacteria physical appearance
Slightly curved, beaded bacilli
What makes mycobacteria resistant to gram stain?
High lipid content with mycolic acid in cell walls
Ziehl-Neelsen stain process
Red Carbol fuchsin addedWashed with acid/alcohol (mycobacteria are acid fast so resistant to destaining)Add Methylene blue
How many bacilli are needed for a diagnosis
10 000 bacilli per ml of sputum
Characteristics of mycobacteria
Aerobic, non-spore forming, non-motileCell wall has high molecular weight lipids
Key components of mycobacteria cell wall
Mycolic acidsLipoarabinomannan
How fast do mycobacteria grow
M. tuberculosis generation time is 15-20h vs. 1h for common bacterial pathogens - Have to wait at least 48 hours before you can declare no M. tuberculosis is growing in a culture - Slows down diagnosis
What is generation time?
Time taken for bacterial population to double in number
How is TB transmitted
aerosol transmission
What occurs in primary TB?
Initial contact made by alveolar macrophagesBacilli taken in lymphatics to hilar lymph nodes
What is latant TB
Where Primary infection is controlled but cell mediated immune response from T cells persitsNo clinical disease (as immune system is strong enough to keep bacilli trapped in granulomas)Cell mediated immune response to TB can still be detected via tuberculin skin testCan remain in the body in this form for decades
What occurs in Pulmonary TB
Can be post-primary (immediately after primary infection) or after reactivationGranulomas form around bacilli that have settled in the apex of lungs * more air and less blood supply (fewer white blood cells)Necrosis occurs in granuloma/tubercles (looks kasiated - like cheese) resulting in abscess formation and caseous material coughed upMay spread in lungs causing other lesions
What are granulomas dependant on
A sufficient number of CD4 cells and TNF alpha being present
What increases risk of TB becoming active
ImmunosuppressionAnti-TNF therapies (given for chronic inflammation)
What is a primary complex in TB
Consists of granuloma, lymphatics and lymph nodes
What issues can TB cause when it spreads beyond lungs
TB meningitisMiliary TBPleural TBBone and joint TBGenito-urinary TB
How can TB be spread beyond lungs
Carried by macrophages which then move around body
What does TB of spine cause?
Bent gibbus formation
Immunological response to mycobacteria
Mycobacteria phagocytosed by macrophages and attempted to phagolysosomeMycobacteria have adapted to intracellular environment and aims to withstand phagolysosomal killing and escape to cytosol
What does effective immunity to M. TB require
CD4 T-cells (this immune response is t cell and macrophage mediated)CD4 generate interferon gamma (IFN-y) - this helps activate intracellular killing by macrophages; and other cytokines like TNFa
What does the granuloma consist of
Macrophages and Th1 lymphocytes capable of synthesysing IFN-y and other cytokines like TNF alpha
What happens if TB granuloma works? What happens if it doesn’t work?
Mycobacteria shut down metabolically in order to survive - dormancyBut if fails, e.g. in the lung, this can result in the formation of a cavity full of live mycobacteria and eventual disseminated disease (can lead to abcesses eventually)
What needs to be done first when trying to culture mycobacteria
Decontamination to kill off other rapid growing bacteria (lipid coat protects mycobacteria)
What methods can be used to culture mycobacteria
Solid cultures- Egg based Lowenstein Jensen- Agar based Middlebrook 7H11- Take 2-8 weeksLiquid culture- Automated systems BACTEC- Mycobacterial growth indicator tube (MGIT).- Fluorometric detection in liquid media- Takes 1-3 weeks
What allows more rapid diagnosis of mycobacteria
Nucleic acid detection (with PCR)(GeneXpert MTB/RIF cartridge based test)
Name of Nucleic acid detection test used for mycobacteria
GeneXpert MTB/RIF cartridge based test(learn name, was highlighted by lecturer)
What does the GeneXpert MTB/RIF cartridge based test do
Purifies and concentrates MTB, sonicates to release genomic material and then performs PCR Detects Rifampicin resistance using fluorescence
How many bacilli/ml (minimum) can GeneXpert MTB/RIF cartridge based test for mycobacteria detect?
131 bacilli/ml
How sensitive and specific is GeneXpert MTB/RIF cartridge based test for mycobacteria?
Sensitivity 88%, Specificity 98%(learn the sensitivity, it was highlighted by lecturer)
Is M. TB fastidious?
yes
When may nucleic acid detection of TB not pick up on TB
if TB is latent
How can latent TB be recognised
Via tuberculin/Mantoux testBit of TB protein is injected into skin (intradermal)If previously infected TB memory cells will be present so skin will become inflamedSimilar test can be done with blood in solution
What is the downside of tuberculin/Mantoux test
Can pick up on the person having had a TB vaccination (presence of antibodies doesn’t necessarily mean they were infected)
How quickly is T cell response stimulated after exposure to M. TB
3-9 weeks
Positive and negative effects of T cell response stimulation in TB
+ve effects; - macrophage killing of mycobacteria ,- containment of infection, - formation of tissue granulomata.-ve effects; - hypersensitivity reactions with skin lesions, - eye lesions - swelling of joints
Standard drug therapy for TB
isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA) and ethambutol (ETH) x 2 months followed by isoniazid and rifampicin for further 4 months
Second line treatment for TB
Injectable agents (streptomycin, cycloserine, capreomycin)- Severe side effects, including liver damage
How long does TB treatment take
4-9 months of combination therapy
What are the resistance mechanisms of M. TB to drugs
Drug inactivation:- Mtb produces beta- lactamaseDrug titration:- Target overproductionAlteration of drug target:- Missense mutationsAltered cell envelope:- Increased permeability and drug efflux
Multi-drug resistant TB: cause and characteristic
Resultant from inadequate TB therapy and failure to clear patients of bacteriaXDR-TB: resistant to four commonly used TB drugs. 6% of all TB cases
Treating XDR-TB
Lengthy and expensiveBPaL regimen:- Bedaquiline - Pretomanid - Linezolid- All orally administered for 6 monthsBPaL can also fail with totally drug resistant TB- No known solution
How do viruses cause disease
- Direct destruction of host cells- Modification of host cell- “Over-reactivity” of immune system- Damage through cell proliferation- Evasion of host defences
What is the leading cause of death world wide
Lower resp tract infection (e.g. can be caused by Respiratory Syncytial Virus)
Importance of viral infections in the UK
- Outbreaks (e.g. Influenza, Measles, Mumps, Norovirus)- Cancer (e.g. EBV and lymphoma, Hep B/C and hepatocellular carcinoma, HPV and cervical/anal cancer, HIV and many resulting infections)- Immunosuppressed patients (Reactivation of latent viruses)- Miscarriage and birth defects (e.g. CMV, VZV, HSV, Rubella)- Morbidity and mortality (Psychological and physical)
Which viruses can lie latent and reactivate upon immunosuppression
All herpes class viruses:- EBV,- CMV,- human herpesvirus 6 (HHV6),- human herpesvirus 7 (HHV7),- JC virus (human polyomavirus 2),- BK virus (human polyomavirus 1
Which viruses are herpes class
- Herpes simplex virus 1 - Herpes simplex virus 2- Varicella-zoster virus- Cytomegalovirus- Epstein-Barr virus- Human Herpesvirus 6 (varients A and B)- Human Herpesvirus 7- Kaposi’s sarcoma virus AKA human herpesvirus 8
What is a virus?
An infectious, obligate intracellular parasite comprising genetic material (DNA or RNA) surrounded by a protein coat and/or a membraneAll also have a receptor binding protein to “dock” to cells
Range of sizes of human viruses
20 to 260nm in diameterPoxviruses are some of the biggestParvovirus is the smallest
Viruses vs Bacteria
- Bacteria have cell wall, viruses don’t- Bacteria have organelles, viruses don’t- Bacteria have DNA and RNA, viruses only have DNA or RNA- Viruses are always dependant on a host cell, bacteria are not- Bacteria are living organisms, viruses are typically considered not living
Are DNA or RNA viruses typically hardier
DNA viruses
What are virions
The complete, infective form of a virus outside a host cell consisting of genetic material (DNA or RNA) and a protein coat/capsid
Different shapes of viruses
- Helical (spiral shaped genetic material)- Icosahedral (cubic? Looks like those regular 3D shapes they make with paper for maths class)- Complex (e.g. bacteriophage looks like a weird spider creature)
Different types of viral external structure
- Non-enveloped (e.g. adenovirus, parvovirus)- Enveloped (e.g. Influenza, HIV)
What would you examine when detecting a new virus
Genetic sequence
Stages of viral replication
- ATTACHMENT to specific receptor2. CELL ENTRY3. HOST CELL INTERACTION and REPLICATION4. ASSEMBLY OF VIRION5. RELEASE OF NEW VIRUS PARTICLES
What does the attachment receptor of a virus dictate
Dictates the type of cells the virus can infect- E.g. gp120 receptor on HIV allows it to attach to CD4 cells with CCR5 or CXCR4 chemokine receptors as coreceptors
What happens during cell entry by a virus
Virion is uncoated within the cellOnly central viral “core” (nucleic acid and some associated proteins) is used for replication
What happens during host cell interaction and replication of a virus
- Viral genome migrates to cell nucleus- Viral genome is transcribed to mRNA using host material (enzymes, amino acids, nucleotides)- Subverts host cell defence mechanism (as it is using own resources)
What does translation of viral mRNA produce
- Structural proteins- Viral genome- Non-structural proteins e.g. enzymes
Where can assembly of virion occur within host cell
- Nucleus (e.g. like herpes viruses)- Cytoplasm (e.g. like poliovirus)- At cell membrane (e.g. influenza virus)
How can new virus particles be released from host cell?
- Particles can burst out causing cell death e.g. like rhinovirus- Particles can bud off/exocytose, taking some of cell membrane with it e.g. HIV, Influenza
Example of direct destruction of host cells by a virus
Poliovirus - causes host cell lysis and death after viral replication period of 4 hoursAs polio affects neurons - this neuronal lysis/death leads to paralysis
Example of virus causing disease by modification of host cell
Rotavirus - atrophies villi and flattens epithelial cells- Decreases small intestine SA- Nutrients including sugar not absorbed- Hyperosmotic state- Profuse diarrhoea
Example of a virus causing disease via “over-reactivity” of immune system
Hep B- Causes hepatocytes to be attacked by cytotoxic T lymphocytesResults in: - Jaundice- Pale stool- Dark urine- RUQ (right upper quadrant abdominal) pain- Fever and malaise- Itching (from release of bile salts)When Hep B is chronic the sustained viral replication and hepatocyte destruction occurs at a lower level so has fewer clinical symptoms(also SARS-Cov-2)
Example of virus causing damage through cell proliferation
HPV causes cervical cancer- After acquisition through direct contact there is partial viral replication and expression of some HPV proteins- Viral DNA is integrated into host chromosome- This leads to continuous expression of oncoproteins causing cellular DNA mutations- And so we get dysplasia and neoplasia
Example of virus causing damage through evasion of host defences
At a cellular level:- Latency e.g. herpesviridae- Cell-cell spread e.g. measles, HIVAt molecular level- Antigenic variability e.g. Influenza, HIV, rhinovirus- Prevention of host cell apoptosis e.g. herpesviridae- Downregulation of interferon and other intracellular host defence proteins (many viruses do this)- Interference with host cell antigen processing pathways e.g. herpesviridae, measles, HIV
Where does each of the main herpes viruses lie dormant
- HSV 1 and 2 and VZV lie latent in Nerve root ganglion- EBV and HHV-8 (AKA Kaposi sarcoma virus) - Lymphoid cells- HHV-6, HHV-7, CMV - lie latent in Myeloid cells
What are the advantages of direct cell-cell spread
- Avoids random release into environment- Increased speed of spread within tissues- Avoiding immune system
What is antigenic variability
Ability to change surface antigens to evade host immune systemThrough mutations during replication
How does prevention of host cell apoptosis by virus cause damage
Prevention of host cell apoptosis allows the virus to continue replicating within it, so more virus is produced and then released. It also has an essential role into how some viruses are oncogenic
How does downregulation of interferon and other intracellular host defence proteins by viruses cause damage
- Normally interferon is synthesised and allows messaging to other cells to activate their antiviral state - When interferon synthesis is blocked, it leaves the neighbouring cells susceptible to infection
How can viruses interfere with host cell antigen processing pathways
Can down regulate MHC class 1 so the viral antigen is not identified quickly by immune system
Why can viruses vary in the range of clinical syndromes they cause
- They can infect different host cells and tissues- They have different methods of interaction with the host cell
What symptoms can they cause: Herpes simplex virus vs JC virus
HSVSkin: - Orofacial herpes- Genital herpes- Herpetic whitlow- Erythema multiforme- Herpes gladiatorumVisceral:- Oesophagitis- Pneumonitis- HepatitisCNS: - Meningitis- Encephalitis- Transverse myelitisEye: - Conjunctivitis- KeratitisJC virus:CNS - Progressive multifocal leukoencephalopathy
Which viruses can cause common cold
- Rhinovirus- Parainfluenza virus- Respiratory syncytial virus
Which viruses can cause eye infections
- Herpes Simplex- Adenovirus- CMV
Which viruses can cause Encephalitis/meningitis
- JC virus- Measles- LCM virus- Arbovirus- Rabies
Which viruses can cause pharyngitis
- Adenovirus- EBV- CMV
Which viruses can cause gastroenteritis
- Adenovirus- Rotavirus- Norovirus- Astrovirus- Coronavirus
Which viruses can cause skin infections
- VZV- HHV-6- Smallpox- Molluscum contagiosum- HPV- Parvovirus B19- Rubella- Measles- Coxsackie A virus
Which viruses cause sexually transmitted diseases
Herpes simplex type 2HPVHIV
Which viruses can cause gingivostomatitis
Herpes simplex type 1Gingivostomatitis = Infection of mouth and gums that leads to swelling and sores
Which viruses can cause pneumonia
Influenza virus type A and BParainfluenza virusResp syncytial virusAdenovirusSARS coronavirus
Which viruses can cause Myelitis
Poliovirus(HTLV-I)
Which viruses cause pancreatitis
Coxsackie B virus
Which virus can cause cardiovascular infection
Coxsackie B virus
What are the diagnostic tests for detecting viruses
- PCR (detects presence of genetic material and the initial size of viral load - doesn’t work for novel viruses)- Serology (Checks for viral exposure. Is there immune memory to the virus)- Histology (any features of viral infection present?)- Viewing a viral culture through light microscopy (structure of infected cells visibly changes) - Limited clinical use- Electron microscopy - Limited clinical use * Too much time/effort, too expensive
Key points about viruses
- Viruses are a COMMON AND SIGNIFICANT cause of human disease globally and nationally (in UK)- Viruses are very SMALL and consist of GENETIC MATERIAL surrounded by a PROTEIN COAT- A virus is COMPLETELY DEPENDANT on host cell machinery to replicate- Recognising how viruses cause disease allows us to: - Understand transmission and natural history - Know who is most at risk - Develop treatments and “preventative” drugs- Viruses vary wildly in range of clinical syndromes they can cause (infect diff cells/tissues AND diff methods of interaction with host)
What does the Varicella Zoster Virus cause
Varicella “chickenpox” - primary infectionHerpes zoster (HZ) “Shingles” - secondary reactivation* Very infectious
What does a VZV particle consist of
- Double strand DNA genome- Nucleocapsid- Tegument (cluster of proteins lining space between envelope and neucleocapsid)- Lipid envelope- Glycoprotein spikes
Infection timeline of VZV
- VZV enters body- Incubation period (1-3 weeks)- Rash- High infectivity period occurs 1-2 days before rash appears to when the blisters have crusted over
When is chickenpox most infectious
1-2 days before rash appears to when the blisters have crusted over
Where does VZV replicate in body
Nasopharynx - present in nasal secretions
How can VZV be transmitted
- Nasal secretions e.g. sneezing- Contact with vesicular matter
Epidemiology of chickenpox
- Common in childhood- Highly contagious, (90% in household hit rate)- Usually benign but can be serious in certain groups 90% of adults raised in the UK have had chickenpox
Risk groups for chickenpox
- Immunocompromised and patients who have had transplants - Adults- Pregnant women- Smokers- Infants
Socioeconomic issue of endemic/chronic illnesses
Lots of lost school days and sick days from workDecrease productivity
Progressive stages of chickenpox blister
- Macule - red spot, not prominently raised- Papule - slight raised bump- Vesicle - small blisters- Pustule - pus-filled, white blisters- Crust - rougher, scabbing
Distribution of chickenpox rash
- More central - rash forms in warmer areas so sparser on extremities- Lesions at different stages of progression can appear on body
Characteristics of smallpox rash
- Centrifugal distribution - more appears on face and extremities (away from centre)- All lesions evolve at same time (so all at same stage of progression)- Deeper lesions, affecting deeper layers of skin - some have central umbilication (dip in middle
What is something that is pathognomonic to chickenpox
Cropping - having lesions at different stages but in the same area of body
Diagnosis of chickenpox
- Pop lesion with sterile needle- (DON’T wipe with alcohol swab first - can denature virus)- Absorb vesicle contents onto swab- Replace swab in cassette and send for VZV/HSV PCR
Complications of chickenpox
- Dehydration- Haemorrhagic change to the rash- Cerebellar ataxia (common) - unsteady gait- Encephalitis - confused, diorientated, loss of motor function, possible sizure- Varicella pneumonia- Bacterial empyema (pockets of pus collected inside body cavity - esp pleural space)- Skin and soft tissue infection typically with group A strep- Bone and joint infections: deep sepsis-osteomyelitis/pyomyositis- Congenital (foetal) varicella syndromeRARE in children - MORE COMMON in adults
What is the most common complication of chickenpox in adults
Chickenpox pneumonitisAffects 15% of healthy adults30% risk in lung disease/smoker30% mortality untreated6% mortality even with treatment
Treatment for Varicella pneumonitis
- Antiviral - Acyclovere (10mg per kg, 3 times a day - IV*) * doesn’t work well orally- Valacyclovere (valine sidechain) when getting better (can be taken orally)
How common is foetal infection of VZV in pregnancy
10-15%~2% develop FOETAL VARICELLA SYNDROME (FVS) when mother contracts chickenpox in FIRST HALF of pregnancy (v rare)
Characteristics of foetal infection of chickenpox
- Usually transient (only lasts short amount of time) and asymptomatic- If any manifestations - usually shingles in first year of life
Potentially severe defects that can occur as complications of FVS
- Cicatricial skin scarring (scarring from formation + contraction of fibrous tissue in wound)- Limb hypoplasia (poorly developed limbs)- Visceral/ocular lesions- Microcephaly (small head) and growth retardation
How are serum samples collected
- Blood sample taken- Tube contains gel to separate cells from serum once centrifuged- Small sarstedt (name of brand) tubes kept for around 3 years (archive samples)
When are initial serum samples taken in pregancy
~10-12 weeks pregnant
Why are archived serum samples useful
Can compare archived serum sample when taking sample later to check for stuff
How does shingles reactivate as a unilateral rash
- First - primary infection of widespread chickenpox- VZV goes dormant in dorsal root (or cerebral) ganglion- Localised reactivation - singles (only affects that dermatome unilaterally as virus can’t cross over midline to other side of spine)
What type of viruses is dormancy and reactivation more common in
DNA viruses
Characteristic onset of shingles
Most common in elderlyCan go from no rash to horrible rash in day or so
Pain relief for shingles rash
- Regular analgesia doesn’t work properly - Have to use drugs that dampen nerve tips (normally used for epilepsy)- E.g. Gabapentine
Sites of shingles reactivation
- Thoracic region (50-70% of all cases)- Cervical, lumbar and sacral - less frequent- Ophthalmic (10-20%) - affecting ophthalmic division of trigeminal nerve - particularly problematic as shingles can affect every layer of eye + cause vision problems
Long term complication of shingles (even after the infection is resolved)
Post-herpetic neuraligia- Nerve endings stay irritated for 2 years or so after the rash is gone
What is the Hutchinson sign and what does it indicate
A lesion on the tip of the nose- Indicates the shingles probably has corneal involvement
Complications/signs of shingles becoming complicated
- Dissemination- Haemorrhagic change- Shingles in peripheral dermatomes - means immune system isn’t controlling things wellIn Immunocompromised - can get SECONDARY infection (e.g. bacterial)
Complications of herpes virus in people with atopic dermatitis/eczema
Eczema herpeticum- Rash looks like it’s never quite come under control- Seems like a combination of herpes virus and rapidly worsening eczema
What do enteroviruses cause
Hand foot and mouth disease- Shed enteroviruses in stool
What pathologies cause rash on palms and soles of feet
- Enteroviruses (hand, foot, mouth disese)- Secondary syphilis (bacterial)- Part of an immune response to drugs - toxic erythema (erythema is just like bruising)
What does Parvovirus B19 target and basic method of action for how they do this
Immature red cells- They attach to P antigens displayed by immature red cells which prevents normal maturation
Complications of parvovirus B19
Profound anaemia - blood cells not replaced as older cells die* Better prognosis in childrenComplications in pregnant women:- Hydrops fetalis - severe swelling in foetus
Treatment for hydrops fetalis
Can give trans umbilical transfusion to increase chance of survival till birth - then supportive measures e.g. assited breathing, removal of excess fluid via needle- Intervention only works in early stages
How do you test for hydrops fetalis
Middle cerebral artery dopplers (detects resistance of flow in foetal brain circulation)
Characteristics of parvovirus B19 rash
- Reticular rash (net-like pattern) - Flares up in higher temperatures e.g. in hot bath
What rash does HHV-6 cause
Roseola - larger, more spread-out patches of slightly raised, darker skin
Characteristics of HSV rashes
- Vesicular rashes - Lesion on vermillion border of lip - common sight of herpes rash - Rashes below belt as well
Typical locations of HSV1 and HSV2 rashes
- HSV1 - both above and below belt- HSV2 - typically only below belt
Complications of HSV in immunosuppressed patients
Mucositis- Sore areas in mouth - mucosal epithelium is shedBugs can target these shed areas - secondary infectionsE.g. candida plaques
Name a common pox virus, especially in children
Moluscum contagiosum- CAN ALSO BE BE SEXUALLY TRANSMITED (in genital areas)
How can moluscum contagiosum be treated
- Pop vesicle and remove white centre- However, if too rough, can cause further skin damage and it can come back
Which part of moluscum contagiosum often reactivates in immunosuppressed people
Lesions around eyes
Which age group is primary cytomegalovirus infection most common in
Teens and 20s
Diagnostic appearance of Primary CMV
Macular rashLymphadenopathy- Atypical lymphocytes (sticky, destructive, spread out)
Complications of CMV reactivation
- Retinitis - pizza pan retina - sight threatening- CMV pneumonitis (most viral pneumonitis look very similar/same) - dangerous- Colitis with CMV on top
Histological hallmark of CMV
Owl’s eye intranuclear inclusions- NORMALLY TREATED WITH PCR tho
How is CMV treated
IV ganciclovir- Or Valganciclovir can be orally taken in less severe case (val is just valine group which allows oral consumption)
What does measles cause
- Cough, coriza (runny nose), conjunctivitis, diarreah- Maculopapular rash (dry feel)- Salt grain-like lesions in mouth- Febrility- Otitis media (can cause hearing loss in severe cases)- Potential pneumonia- Potential encephalitis
What do the local health protection unit control
Cough, coriza, conjunctivitis, diarreah, immune control
How transmissible is measles
R0 = 16 (very high)100 in unvaccinated population
Characteristic skin presentation of Dengue shock syndrome
Significant bruises/swelling from internal bleeding
Which gram +ve bacteria can cause cellulitis
S. aureus and Group A (pyogenes), C, G strep
Which gram +ve bacteria can cause pharyngitis/strep throat
Group A, C, G strep
Define protozoa
Single cell with nucleus - is eukaryotic>30, 000 specieses
What are the 5 major groups of protozoa
FlagellateAmoebaSporozoaMicrosporidiaCiliate
List main flagellate protozoa
- Trypanosoma brucei gambiense (African trypanosomiasis - sleeping sickness)- Trypanosoma brucei rhodesiense (African trypanosomiasis - sleeping sickness)- Trypanosoma cruzi (American Trypanosomiasis - Chagas Disease)- Leishmania spp. (Leishmaniasis)- Trichomonas vaginalis (Trichomoniasis - STI)- Giardia lamblia (Giardiasis)
Which protozoa cause African trypanosomiasis?
- Trypanosoma brucei gambiense- Trypanosoma brucei rhodesiense(Batman puts you to sleep by stabbing with a needle in gambia or rhodes)
Which organism transmits African trypanosomiasis
Tsetse fly (via bite)
What does African trypanosomiasis cause
- Chancre- Flu like symptoms- CNS involvement (sleepy, confusion, personality change)- Coma and Death
How is African Trypanosomiasis diagnosed
Via blood film or CSF
Which protazoa causes American trypanosomiasis (Chagas disease)
Trypanosoma cruzi(Jesus got nailed to a cross - people felt ill)
How is american trypanosomiasis spread
- Through contact with faeces of triatomine “kissing” bug (found around/in mud huts in South America)- Through blood- Vertically acquired- Eating contaminated food
Symptoms of American Trypanosomiasis (Chagas disease)
Acute:- Flu like symptoms- Lymphadanopathy - (Romaña sign - swollen eyelid - if faeces rubbed into eye)- (Chaga means fester/disease in Portuguese)Chronic:- Cardiomyopathy (harder to pump - walls of heart: stretched, thickened or stiff)- Megaesophagus (oesophagus dilates and loses motility)- Megacolon (dilation)
How is Chagas disease diagnosed
- By visualising trypomastigotes (the type of flagellate protozoa that causes Chagas) on blood film- OR amastigotes (the protozoa have no visible flagellum!) on biopsy (for CHRONIC)Remember as: they need flagella (masti) to move around if only temporary (i.e. acute) but Chagas requires maturity in life which causes you to keep most of your potential inside so trypomastigote not promastigote. When it is chronic the -mastigotes get comfortable and stop moving around (thus no VISIBLE flagella - promastigote)
Important types of trypanosomatida
- Amastigote - no visible flagella (but potential for flagella still there)- Promastigote - anterior flagella (cell itself looks like cover of edamame beans/pea pod) with flagellum STICKING MOSTLY out of the cell- Trypomastigote - Still bean pod looking cell with anterior flagella but most of the flagellum is now INSIDE the cell but at the edge i.e ATTACHED PARALLELY TO CELL MEMBRANE
Can Chagas disease be treated
Can be treated effectively if acuteCANNOT effectively treat once chronic - can only provide supportive treatments e.g. pacemaker, antiarrhythmias etc.
Which organisms cause Leishmaniasis
Leishmania! Spp. (means specieses - >20 affect humans) - protazoa(Lesion mania - in the sand)
How is leishmaniasis spread?
Via bite of sand fly
How is Leishmaniasis diagnosed
- Via biopsy (can see amastigotes)- Via serology combined with clinical signs- Can be diagnosed with PCR
What are the 3 clinical pictures of Leishman
- Cutaneous- Mucocutaneous- Visceral(baso increasing severity from superficial to deep - also gets more virulent with increasing severity)
What does cutaneous Leishmaniasis cause
Most commonUlcers on exposed body parts e.g. face, arms, legsMay be large number of lesions (can be up to 200 - can cause serious disability)Risk of superadded infectionsCauses scarring -> social prejudice (thus better to get bitten in less exposed areas)
What does mucocutaneous Leishmaniasis cause
Partial/total destruction of mucous membranes of:- Nose- Mouth- Throat cavities- And tissues surrounding these sitesSocial stigma and rejection!Increased risk of recurrent bacterial pneumonia (people can subsequently die of sepsis) due to destruction of nose/palate
What does Visceral Leishmaniasis cause
Affects lymph system so:- Irregular bouts of fever- Weight loss- Massive splenomegaly- Hepatomegally- Anaemia (secondary)- High fatality if untreated (100% within 2 years)
Which organism causes trichomoniasis
Trichomonas vaginalis - protozoaSTI ENDEMIC TO UK
Trichomoniasis signs/symptoms
- Often asymptomatic- Dysuria- Yellow, frothy discharge
How can Trichomoniasis be treated
With metronidazole - antibiotic
What organism causes Giardiasis + type of spread
Giardia lambliaFaeco-oral spread esp linked to contaminated water
Giardiasis signs/symps
DIarrhoeaKEY FEATURES: Cramps, bloating, flatulenceCan become lactose intolerant after infection
Where is giardiasis more likely to occur
In a traveller In childcare settings e.g. nurseriesThese are KEY FEATURES
How can giardiasis be diagnosed
Trophozoites (active - jellyfish with face)/cysts (inactive - round, thick wall) seen in stoolIdentifying clinical features
How is giardiasis treated
Metronidazole - antibiotic
What is the name of the main medically relevant amoeba? What disease does it cause? + spread
Entaemoeba histolytica (Amoeba that affects gut and destroys cells)Causes Amoebiasis (Amoebic dysentry! Bloody diarrhoea!)FAECO-ORAL SPREAD
What does amoebiasis cause?
IMPORTANT:- Dysentry- Colitis- Liver and lung abscesses- Can live in gut asymptomatically
How do amoeba move
They use pseudopoda - temporary projections of the cell - kinda just reach out with protrusions and squirm along like macrophages
Why do entamoeba histolytica cause intestinal issues
The amoeba invades colon and consumes RBCs
Risk factors for Amoebiasis
- Poor sanitary conditions/tropical countries- MSM (men who have sex with men)
How can amoebiasis be diagnosed
Trophozoites/cysts seen in stool
How is amoebiasis treated
METRONIDAZOLE
Name the main sporozoa
- Cryptosporidium spp (Spore-like protozoa that affects crypts in intestine)- Toxoplasma gondii (remember as Toxic in plasma?)- Plasmodium spp (need to learn individual spp. - related to blood plasma)
What disease does Cryptosporidium spp cause? Which species in particular are relevant in humans
Cryptosporidiosis (diarrhoeal)- C. Hominis and C. parvum (Homo species affecting and ‘small’ respectively)
What are the symptoms of Cryptosporidiosis
- DIARRHOEA (watery but no blood)- Vomiting- Fever- Weight loss- Usually self-limiting but can be fatal in - immunocompromised
How can cryptosporidiosis be diagnosed
Acid fast oocysts seen in stool
How is Cryptosporidiosis spread
Waterborne (e.g. Fresh water swimming)
How long does cryptosporidiosis last in healthy individuals
Usually 1-2 weeks
What is cryptosporidiosis treated with in more severe cases
Nitazoxanide - antimicrobial
What organism causes Toxoplasmosis?
Toxoplasma gondii (toxic plasma gon’ die?)
How is Toxoplasmosis acquired?
- Ingestion of food contaminated with bradyzoits (tissue cysts) - e.g. rare beef/lamb, shellfish, unpasturised goats milk- Ingestion of oocysts via contact with FELINE faeces
Toxoplasma gondii - what are their definitive hosts and intermediate hosts
- Only cats are definitive hosts (full cycle occurs, ingestion to excretion)- Other mammals including humans are intermediate hosts (parasite can be ingested but it becomes a tissue cyst so isn’t excreted)
What occurs when toxoplasma gondii oocysts/bradyzoites are ingested
- Haematogenous spread- Invasion of tissues- Tissue cysts develop, primarily in muscles and neurons
What can toxoplasmosis cause in immunocompromised
- Disseminated disease - Toxoplasma Encephalitis (inflammation of brain)- Chorioretinitis (inflammation of choroid lining of retina)- Can have devastating consequences in pregnancy: - Worst in first trimester - Causes congenital toxoplasmosis - Microcephaly - Hydrocephalus - Interuterine growth retardation - Miscarriage - Can be treated if picked up early enough - Counselling for termination may be offered
Presentation of acute toxoplasmosis in healthy individual
- 90% often asymptomatic- 10% - glandular fever type illness
Which organism causes Malaria?
Plasmodium spp - sporazoa protozoa- Plasmodium falciparum (most SEVERE, high mortality if untreated - through blood plasma - falciparum = small scythe)- Plasmodium ovale- Plasmodium vivax- Plasmodium malariae- Plasmodium knowlesi
Incubation period for common malaria causing sporozoa
- Plasmodium falciparum - typically a month- Plasmodium ovale and vivax - up to a year
Which organism transmits malaria
Female Anopheles mosquito
How is malaria diagnosed?
- Light microscopy of blood film - will contain trophozoite- Thick and thin film done- Three blood films done on consecutive days (length of lifecycle)- First smear probs +ve in 95% of cases- Can also used rapid diagnostic tests that detect plasmodium antigens in blood
Thick vs. thin blood films
- Thick film is sensitive but low res (e.g. for deciding if person has malaria or not)- Thin film higher res so can identify different species AND is used to work out parasitaemia percentage
Symptoms of malaria
- FEVER!!- Chills- Headache- Myalgia- Fatigue- Diarrhoea- Vomiting- Abdo painCan be variable in diff people but fever is most common
Malaria signs
- Anaemia- Jaundice- Hepatosplenomegaly- ‘Black water fever’ (haemoglobinuria) - from haemolysis products in urineSome people may not LOOK ill
Who are most at risk of getting the most unwell from malaria
Travellers and pregnant women
Life cycle of malaria
- Mosquito ingests plasmodium gametocytes from biting infected human (is infected for rest of its 4 week lifespan)- Gametocytes develop in mosquito midgut and end as sporozoites in salivary glands - MOSQUITO BITES next human and injects sporozoites- Sporozoites now in human blood infect HEPATOCYTES - Infected hepatocytes develop into SCHIZONTS, which burst and infect RBCs causing ABDO PAIN- Plasmodium becomes trophozoite within RBC- Trophozoite develops into schizont which ruptures and re-infects more RBCs (causes CYCLICAL FEVER)- Causes HAEMOLYSIS so ANAEMIA and JAUNDICE (from BILIRUBINEMIA) and HAEMOGLOBINURIA- Blood stage usually lasts 48 hours- Some trophozoites develop into gametocytes which are taken up by another mosquito!
What additional ability makes Plasmodium falciparum infection more severe + it’s complications
- Causes OBSTRUCTED MICROCIRCULATION (typically in big organs) - Mostly due to PROINFLAMMATORY CYTOKINE CASCADE - stimulates endothelial activation which causes rolling of RBCs and endothelial cytoadherence - Also causes ROSETTING - clumping together of RBCs and plateletsResults in “Complicated Malaria”- Cerebral malaria, - ARDS, - Renalfailure- Bleeding/Anaemia- Sepsis/Shock- Possibly other organ failure including heart - esp because of anaemia -> anaerobic -> LACTIC ACIDOSIS + HYPOGLYCAEMIA (reduced gluconeogenesis from liver damage + parasite uses up glucose)
Causes and signs/symptoms of Cerebral malaria
VASCULAR OCCLUSION causes:- DROWSINESS- RAISED INTRACRANIAL PRESSURE- SEIZURES- COMA -> deathDrowsiness can also be due to hypoglycaemia so check that too
Causes and signs/symptoms of Acute Respiratory Distress Syndrome (ARDS!) due to complicated malaria
Direct effect of VASCULAR OCCLUSION:- Compensatory TACHYPNOEA due to ANAEMIA and LACTIC ACIDOSIS- INCREASED VASCULAR PERMEABILITY causing PULMONARY OEDEMA- All contribute to SOB and HYPOXIA
Causes and signs/symptoms of Renal failure in complicated malaria
Directly due to VASCULAR OCCLUSION- Secondary HYPOPERFUSION due to DEHYDRATION from fever (which causes HYPOTENSION)- HAEMOLYSIS products can be NEPHROTOXICSubsequently:- PROTEINURIA- FATIGUE- HAEMATURIA
Causes of Bleeding in complicated malaria
- Platelet aggregation occurs which causes THROMBOCYTOPENIA- Generalised inflammation -> activation of coagulation cascade -> clotting factors used up -> DISSEMINATED INTRAVASCULAR COAGULATION (DIC) -> micro clots in blood and abnormal bleeding e.g. ABNORMAL EPISTAXIS (nose bleed)Worsening anaemia also contributes
Causes of Shock in complicated Malaria
- PRO-INFLAMMATORY CASCADE occurs which causes VASODILATION- SEVERE ANAEMIA can cause CARDIOGENIC SHOCK- INCREASED VASC PERMEABILITY in the bowel can allow gram -ve bacteria from bowel into bloodstream -> causes GRAM -VE SEPSIS- Increased vascular permeability can also cause intravascular fluid leakage into “3rd space”- BLEEDING can cause HYPOVOLEMIA
Signs and symptoms of shock
- HYPOTENSION- TACHYCARDIA- DROWSY- PALE
Treatment for Complicated malaria?
IV ARTESUNATE (combination of quinine and doxycycline)
Supportive measures for the extra complications of Complicated malaria
- Cerebral: antiepileptics- ARDS: oxygen, diuretics, ventilation- Renal failure: fluids, dialysis- Sepsis: broad spectrum antibiotics- Bleeding/Anaemia: blood products- Exchange transfusion if huge parasite burden
How can relapses of malaria occur
P. ovale and vivex can form HYPNOZOITES in liver which can reactivate up to years later
What additional treatment is given to eliminate hypnozoites after p. ovale/vivex infection
- PRIMAQUINE - CONTRAINDICTED in G6PD (glucose-6-phosphate dehydrogenase) DEFICIENCY - can cause HAEMOLYSIS
Example of drug to treat acute malaria (uncomplicated)
Chloroquine
When should you consider a possibility of malaria?
FEVER + RECENT TRAVEL
What is the key principle of antibiotics
Only use antibiotics if they are actually needed
What is an antibiotic
- Agents produced by micro-organisms that kill or inhibit the growth of other micro-organisms in high dilution- Work by binding to a target site on a microorganism- Most agents used now are semi-synthetic derivatives of antibiotics so the more correct term is antimicrobials
Define target site (on a bacterium)
Points of biochemical reaction crucial to the survival of the bacterium
Where can antibiotics bind to bacteria and what defines where they bind
- Crucial binding site varies with the ANTIBIOTIC CLASS- Some bind to ribosomes (affects protein synthesis)- Some bind to DNA or associated components (affects nucleic acid synthesis)- Some bind to cell wall (affect cell wall synthesis)
Which classes of antibiotics affect cell wall synthesis
Beta lactams (contains beta lactam rings)- Penicillins- Cephalosporins- Carbapenems- MonobactamsGlycopeptides
Name the important penicillins
- Penicillin V- Penicillin G (Benzylpenicillin)- Flucloxacillin- Amoxicillin/Ampicillin- Piperacillin
Name the important Cephalosporins
- Cefuroxime- Cefotaxime- Ceftriaxone- (Cefalexin)- (Ceftazidime
Name the important carbapenams
- Meropenem- (Ertapenem)- (Imipenem)
Name a relevant Monobactam
Aztreonam
Name some important glycopeptides
VancomycinTeicoplanin
Which type of bacteria are more susceptible to beta lactams and glycopeptides
Beta lactams and glyopeptides work best on gram +ve as they have big cell wall
Mechanism of action of beta lactams
- Bind covalently (and thus irreversibly) to PENICILIN BINDING PROTEINS- Cell wall synthesis (specifically peptidoglycan production) is disrupted - lysis occurs- Results in HYPO-OSMOTIC or ISO-OSMOTIC environment (fluid moves into cell and causes it to burst)- Only active against rapidly multiplying organisms
Why are gram -ve bacteria less susceptible to beta-lactams
- Beta-lactams have to diffuse through the bacterial cell wall first to bind to the PBPs- Gram negative organism have additional LPS layer that decreases antibiotic penetration
What causes the differences in the spectrum and activity of beta-lactam antibiotics
It is due to their relative affinity for different PBPs
Which antibiotics affect nucleic acid synthesis/DNA functioning
- Rifampicin - METRONIDAZOLE- Fluoroquinolones (acts on DNA gyrase (and topoisomerase IV)) - CIRPROFLUXACIN - Levofluxacin - Moxifloxacin
Which antibiotics affect protein synthesis (at ribosomes)
- Aminoglycosides (30s subunit)- Tetracyclines (works on 30s subunit)- Lincosamides (50s subunit)- Macrolides- Chloramphenicol
What is the main aminoglycoside
GENTAMICIN- used for lots of different serious bacterial infections
What is the main tetracycline
DOXYCLINE (also an antiprotozoal - used against malaria)- commonly used for chlamydia
What is the main Lincosamides
CLINDAMYCIN - commonly used for patients allergic to penicillin
What are the main Macrolides and what are they used for
ErythromycinCLARITHROMYCIN (also used for H. pylori infections)Azithromycin (also used for chlamydia)- commonly used for resp. And throat infections- also in uncomplicated skin infections and otitis media in paediatrics
Which antibiotics affect Folate synthesis
- Sulphonamides (e.g. sulphamethoxazole)- TRIMETHOPRIM - Commonly used for UTIs- CO-TRIMOXAZOLE (combination of sulphamethoxazole and trimethoprim)
What are bactericidal antibiotics
Agent that KILLS BACTERIA by INHIBITING CELL WALL SYNTHESISKill >99.9% in 18-24 hours
What are bactericidal antibiotics useful for
- In infections where penetration to site of bacterial growth is poor (e.g. endocarditis)- In difficult to treat infections (e.g. in immunosuppressed patients)- Or infections that need to be eradicated quickly (e.g. meningitis and encephalitis, sepsis)
Why does endocarditis require bactericidal antibiotics
- Infection is in a site where patient’s own immune system is unable to deal with bacteria- Bacteria are working alone - Bacteria within cardiac vegetations are at high concentrations, have lower rates of metabolism/cell division/are dormant- Surrounded by fibrin, platelets and possibly calcified material
What is a negative side effect of bactericidal antibiotics
- Can lead to release of endotoxin from gram negative bacteria- Resulting increase in antigenic load causes an aggressive and dangerous inflammatory response - gram negative bacterial sepsis- Jarisch-Herxheimer reaction from spirochetes (e.g. in syphilis, leptospirosis etc.)- Also can cause toxin production -> Toxic Shock Syndrome (s. aureus) and Pneumolysin release (s. pneumonia)
What do bacteriostatic antibiotics do
Inhibit bacterial growthKill >90% in 18-24 hour
How are bactericidal and bacteriostatic antibiotics defined (in terms of MBC and MIC)
- If the ratio of Minimum Bactericidal Concentration (MBC) to MINIMUM INHIBITORY CONCENTRATION (MIC) is >4 - the drug is defined as bacteriostatic- If the ratio of MBC to MIC is <4 the drug is defined as Bactericidal
What types of antibiotics are bacteriostatic
Antibiotics that inhibit protein synthesis, DNA replication or metabolism
How is MIC determined
- Test in tube dilution in lab- INCUBATE for 24 HOURS- Determine MIC based on TURBIDITY (how clear or cloudy the solution is)
What does an antibiotic need to be able to do to work effectively
- It needs to attach to its binding target AND occupy an adequate number of binding sites (related to its conc within microbe) - CONCENTRATION present- It needs to remain at the binding site for a sufficient period of time for bacterial metabolic processes to be sufficiently inhibited - TIME it remains
Two types of bacterial killing functioning by antibiotics
Time dependant killingConcentration dependent killing
What is the key parameter for time dependent killing for antibiotics
- The TIME for which serum concs remain ABOVE the MIC during the dosing interval- t>MIC
Which antibiotics use time dependant killing
Beta-lactamsClindamycinMacrolidesOxazolidinones (synthetic - used against resistant bacteria e.g. vancomycin resistant enterococcus, MRSA, M. tb)
What is the key parameter in concentration dependent killing
How HIGH the conc is ABOVE the MICPeak conc/MIC ratio
Which antibiotics use conc-dependent killing
AminoglycosidesQuinolones
Define pharmacokinetics
The activity of drugs in the body over a period of time. It is a function of:- Its RELEASE from dosage form, - ABSORPTION from site of administration into bloodstream, - DISTRIBUTION to various parts of the body, including site of action- its rate of ELIMINATION from body via metabolism (via liver) or excretion (via kidney) of unchanged drug
Questions to ask when considering appropriateness of antibiotics for a certain site
- Which antibiotics will penetrate that site? - E.g. if pus has collected around the infected site there will be no direct blood supply and it will be difficult to get antibiotic to the site. Or in endocarditis as the bacteria is on the valves which depend on blood flowing past so hard to get antibiotic to stick- What is the pH of the site?- Is the antibiotic lipid soluble?
What does dosage interval/duration of antibiotic depend on
Half life + elimination time
How do bacteria resist antibiotics
- Change antibiotic target- Destroy antibiotic- Prevent antibiotic access- Remove antibiotic from bacteria
Give examples of bacterial resistance due to changed antibiotic target
IMPORTANT- Flucloxacillin no longer able to bind to PBP of certain staph aureus (MRSA)- Wall component changes in enterococci reduce vancomycin binding (VRE)- Rifampin activity reduced by changes to RNA polymerase in M. TB (Multi drug resistant TB - MDR-TB)
Examples of bacterial resistance via destroying/inactivated antibiotic
- Some bacteria have ‘BETA LACTAMASE’, an enzyme which HYDROLYSES the BETA LACTAM RING of penicillins and cephalosporins etc.- Staphylococci produce ‘penicillinase’ - inactivates penicillin (BUT NOT flucloxacillin)- Gram -VE bacteria PHOSPHORYLATE AND ACETYLATE Aminoglycosides (e.g. gentamicin)
How do bacteria prevent antibiotic access
Modify the bacterial membrane porin channel size, numbers and selectivity
Examples of bacterial resistance via preventing antibiotic access
- Pseudomonas aeruginosa against imipenem, - Gram negative bacteria against aminoglycosides
Give examples of bacterial resistance via removal of antibiotic from bacteria
- S. aureus or S. pneumoniae resistance to fluoroquinolones- Enterobacteriacae resistance to tetracylines
How do bacteria develop resistance
Intrinsic resistanceAcquired resistance:- spontaneous gene mutation- horizontal/lateral gene transfer ** conjugation ** transduction ** transformation
Characteristic of intrinsic resistance
All subpopulation of a species will be equally resistant
Examples of intrinsic resistance
- Aerobic bacteria CANNOT reduce metronidazole to its active form (requires anaerobic pathway)- Vancomycin CANNOT penetrate outer membrane of GRAM NEGATIVE bacteria- Anaerobic bacteria lack oxidate metabolism which is required for aminoglycoside uptake- PBP in enterococci are not effectively bound by cephalisporins
Example of resistnace via spontaneous gene mutation
M. TB - point mutation in the rifampin-binding region rpoB
What occurs in conjugation (bacterial lateral gene transfer) + example
Sharing of extra-chromosomal DNA plasmids (via “bacteria sex”)New Delhi metallo-beta-lactamase, ESBLs (extended spectrum beta-lactamases)
What occurs in transduction (bacterial lateral gene transfer) + example
Insertion of DNA via organisms like bacteriophagesmecA genes for MRSA are acquired via a mobile genetic element called “staphylococcal cassette chromosome”
What occurs in transformation (bacterial lateral gene transfer) + example
Picking up naked DNA from the environmentForeign DNA from S. mitis to S. pneumoniae conferring penicillin resistance
Mode of resistance of MRSA
- Contains mecA gene - on Staphylococcal cassette chromosome mec (SSCmec) - acquired via transduction mediated by bacteriophage- Encodes PBP2a (penicillin binding protein 2a)- Confers resistance to all beta-lactams including flucloxillin
Resistance acquisition of VRE
- Plasmid mediated - of gene encoding altered amino acid which prevents vancomycin binding- Promoted by cephalosporins
Mode of aquisition + action of ESBL
Acquired via random mutation at active siteHydrolyse OXYIMINO side chains of CEPHALOSPORINS (cefotaxime, ceftriaxone, ceftazidime) and MONOBACTAMS (aztreonam)
