microbiology Flashcards
pathogen
organism that causes or is capable of causing disease
commensal
organism which colonises the host but causes no disease in normal circumstance
opportunistic
microbe that only causes disease if host defences are compromised
pathogenicity
the degree to which a given organism is pathogenic
asymptomatic carriage
when a pathogen is carried harmlessly to a tissue site where it causes no disease
bacterial nomenclature
consists of genus and species
e.g. staphylococcus (genus) aureus (species)
areas that are colonised
most mucosal surfaces
digestive tracr, nasal cavity, skin, urethra, vagina
sterile areas
lungs
gallbladder
kidneys
upper urinary tract
bacterial morphology
divided into coccus (round) and bacillus (rod)
further divided into gram positive or negative
structures in bacteria
inner and outer membrane capsule chromosome of circular DNA pili flagella
differences between gram positive and negative
different cell envelope
negative have 2 membranes and lipopolysaccharides
positive have much more peptidoglycan
bacterial environment
temp= -800 degrees to +80 degrees pH= 4-9
growth of bacteria
lag phase
exponential phase
stationary phase- number of viable bacteria decreases
endotoxin
component of outer membrane of bacteria
exotoxin
secreted proteins
gene mutation
base substitution
deletion
insertion
gene transfer
transformation e.g. via plasmid
transduction e.g. via phage
conjugation e.g. via sex pilus
plasmids
proteins can be synthesised using plasmid DNA
tend to be spread during bacterial conjugation
gram stain steps
- apply primary crystal violet (purple)stain to fixed, heated bacteria
- add iodide which binds to stain and fixes it to cell wall
- decolourise with ethanol or acetone
- counter stain with safranin (pink)
- negative lipids interact with decolouriser and lose their other lipopolysaccharides and crystal violet- iodide (CV-I) so appear pink with counterstain
- positive are dehydrated by decolouriser and the cell wall and CV-I are trapped in the multilayered peptidoglycan so are purple
gram stain of neisseria gonorrhoea
similar appearance to kidney beans with concave sides facing each other
staphylococci gram stain
appear in clusters
catalase test
flavoproteins reduce O2 using superoxide dismutase- producing H2O2
2H2O2 -> 2H20 +O2
staph are catalase + but strep aren’t
coagulase test
distinguishes s.aureus (positive) from other staphylococci (negative)
it activates prothrombin to convert fibrinogen to fibrin
a positive test- clot forms
latex test for staph. aureus
positive= agglutination occurring
haemolysis
ability of a bacteria to breakdown red blood cells in blood agar
requires expression of haemolysin
optochin sensitivity
strep. pneumoniae are optochin sensitive
other strep are resistant
oxacillin disc
the oxacillin disc tests for penicillin sensitivity
resistant strains should have a MIC performed to penicillin to ascertain level of resistance
selective indicator medial for fram negactive bacilli
MacConkey agar
cysteine lactose electrolyte deficient (CLED) media
MacConkey agar
o Bile salts inhibit Gram-positive bacteria and inhibits swarming of a Gram negative
bacterium Proteus spp.
o Crystal violet also inhibits some Gram-positive bacteria
o Neutral red acts as a pH indicator so that bacteria that ferment lactose (Lac+) and
release H+ appear pink or red
o Lactose is available for Lac+ micro-organisms
o Peptone is used by Lac- micro-organisms, resulting in production of NH3 and a rise in pH
cysteine lactose electrolyte deficient (CLED) media
o Electrolyte deficient media prevents swarming of Proteus mirbilis
o Bromothymol blue is indictor, lactose ferementation causes blue to yellow change,
decarboxylation of L-cyteine results in blue colour
o Used as media for urinary pathogens
lactose fermenter on CLED agar
A simple but important method of classifying members of the Enterobacteriaceae is based
upon lactose fermentation. Classically lactose fermenting organisms are E. coli, Klebsiella, Enterobacter and Citrobacter species.
non-lactose fermenter on CLED agar
The non-lactose fermenting organisms usually belong to the genera other than those
mentioned in slide ‘Lactose fermenter on CLED agar’. However, some lactose fermenting organisms, because they are late lactose fermenters, may appear as a non-lactose
fermenter. Late lactose fermenters are recognised by a positive ONPG test.
motility
distinguishes bacteria
flagella staining patterns
swarming motility patterns on agar
oxidase test
-Tests if micro-organism contains a cytochrome oxidase or indophenol oxidase
-Utilises a redox indicator such as N,N,N’,N’-tetramethyl-p-phenylenediamine (TMPD)
-In oxidised state indicator dark blue or maroon
-Implies organism able to use oxygen as the terminal
electron acceptor
3 main types of gram positive bacteria
streptococcus
staphylococcus
corynebacterium
coagulase
enzyme produced by bacteria that clots blood plasma
fibrin clot formation around bacteria protects it from phagocytosis
staphylococcus
coagulase +ve or -ve
s.aureus is most important (coag +ve)
coag -ve are important in opportunistic infections
staphylococcus habitat
nose
skin
MRSA
resistant to: beta-lactams genatmicin erythromycin tetacycline
staph. aureus virulence factors
pore forming toxins
proteases
toxic shock syndrome toxin
protein A
staph. aureus associated conditions
pyogenic- wound infections, pneumonia, endocarditis
toxic mediated- toxic shock syndrome, food poisoning
coag -ve - infected implants, septicaemia
coagulase- negative staphylococci
s. epidermidis
s. saprophticus
s. epidermidis
infections in debilitated, prostheses - opportunistic
main virulence factor is ability to form persistent biofilms
s. saprophticus
acute cystitis
haemagglutinin for adhesion
urease
streptococci classification
haemolysis
lancefield typing
biochemical properties
alpha haemolysis
partial
greening
H2O2 reacts with Hb
e.g. s.intermedius
beta haemolysis
complete lysis
haemolysins O and S
e.g. s.pyogenes
gamma haemolysis
no lysis
some s. mutans
sero-grouping
method of grouping catalase negative, coagulase negative bacteria based on bacterial carbohydrate cell surface antigens
infections caused by S. pyogenes
wound infections tonsillitis otitis media impetigo scarlet fever
S. pyogenes virulence factors
capsule- hyaluronic acid
M surface protein- encourages complement degradation
enzymes
toxins
s. pneumoniae
normally commensal in oropharynx in 30% of people
causes - pneumonia, otitis media, sinusitis, meningitis
s. pneumoniae predisposing factors
impaired mucus trapping
hypogammaglobulinaemia
asplenia
s. pneumoniae virulence factors
capsule
inflammatory wall constituents
cytotoxin
viridans streptococci
collective name for oral streptococci
alpha or gamma haemolytic
some cause dental abscesses
important in infective endocarditis
C. diphtheriae
droplet spread
can grow in the presence of potassium tellurite
C. diphtheriae toxin
inhibits protein synthesis
C. diphtheriae prevention
vaccination with toxoid
most relevant gram negative bacteria
proteobacteria
chlamydiae
spirochaeta
bacteroidetes
proteobacteria
family of enterobacteriacaeae
rods
motile
facultatively anaerobic
e. coli infections
wounds infections UTIs gastroenteritis travellers diarrhoea bacteraemia meningitis
why are some e.coli strains pathogenic
have additional DNA that causes them to be pathogenic
several pathovars, many serotypes or strains
shigella
closely related to e. coli
four species- dysenteriae, flexneri, boydii, sonnei
severe bloody diarrhoea
pathogenesis of shigella
acid- tolerant
person-person or contaminated water and food transmission
invasion of shigella
moves form cell to cell in colonic mucosa
cause damage to mucosa which results in diarrhoea
shigella virulence determinant
shiga toxin- causes cell death by blocking protein
salmonella
two species= enterica and bongori (rare)
salmonella infections
gastroenteritis
enteric fever
bacteraemia
salmonella pathogenesis
- ingestion of contaminated food/water
- invades gut epithelium of small intestine
- intestinal secretory response
- does not produce toxins
- enters submucosa
- intracellular survival/replication
vibrio cholerae
facultative anaerobe
curved rods with single polar flagellum
cholera= most severe diarrhoeal disease
vibrio cholerae pathogenesis
faceal-oral route incubation voluminous watery stools no blood, pus or fever 60% mortality
vibrio cholerae virulence determinants
TCP pili required for colonisation
cholera toxin
pseudomonas aeruginosa
single polar flagellum
opportunistic
antibiotic resistant
pseudomonas aeruginosa acute infections
localised- burns, UTI, keratitis
systemic
ICU patients
pseudomonas aeruginosa chronic infections
cystic fibrosis patients
pseudomonas aeruginosa virulence determinants
twitching motility
multiple toxins
legionella pneumophila
immunocompromised
severe 15-20% mortality
fastidious- charcoal agar
legionella pneumophila pathogenesis
modulates trafficking of phagosome
avoids phagosome-lysosome fusion
differentiate to replicative phase
bordetella pertussis
whooping cough
short rods- coccobacilli
fastidious
non-invasive
bordetella pertussis toxins
pertussis toxin
adenylate cyclase- haemolysin toxin (increases cAMP)
neisseria
non-flagellated diplococci
fastidious
2 species= meningitidis and gonorrhoeae
n. meningitidis
asymptomatic in nasopharynx of 5-10% rises to 20-90% during outbreaks aerosal transmission (person to person)
n. meningitidis pathogenesis
crosses nasopharyngeal epithelium and enters blood stream
enters subarachnoid space after crossing blood brain barrier
n. meningitidis virulence determinants
capsule is major determinant
n. gonorrhoeae
asymptomatic in 30% of females
person-person sexually transmitted
proctitis, gingivitis, pharyngitis
n. gonorrhoeae virulence determinants
twitching motility
non-capsulated
campylobacter
spiral rods
unipolar or bipolar flagella
most common cause of food poisoning
bacteroides
non-motile rods
strict anaerobes
commensal flora of the large intestine is most abundant (30-40%)
most common cause of anaerobic infections
chlamydia
small and non motile
obligate intracellular parasites
many live asymptomatically as endosymbionts
growth cycle of chlamydia
2 developmental stages-
elementary bodies= infectious, enter cell through endocytosis, prevent phagolysosome fusion
reticulate bodies= replicative, non-infectious, possess tubular projections
life cycle of chlamydia
- entry as elementary bodies
- prevent phagolysosome fusion
- conversion into reticulate body
- multiplication
- convert back to elementary body
- cell lysis and release
chlamydia. trachomatis
most common std
can spread to uterus and ovaries
usually asymptomatic
can also cause conjunctivitis- hand to eye
Chlamydophila. pneumoniae
respiratory tract
infects other mammals
Chlamydophila. psittaci
mainly birds
spirochetes
long, slender, helical, flexible
free living and non-pathogenic
modified outer membrane
B. burgdoferi
lyme disease tick borne bull's eye rash spreads through ECM culture in medium containing rabbit serum
T. pallidum
syphilis
primary stage- localised infection, days to weeks
secondary stage- systemic, 1 to 3 months
tertiary stage- gummas in bone and soft tissue, neurosyphilis, several years
Gram-negative pathogens in the respiratory tract
o Bordetella pertussis o Haemophilus influenzae o Pseudomonas aeruginosa o Legionella pneumophila o Chlamydia pneumoniae
Gram-negative pathogens in the GI tract
o Vibrio cholerae o Shigella dysenteriae/S. flexneri o S. enterica sv enteritidis/typhimurium o Some Escherichia coli serotypes o Campylobacter jejuni/C. coli o Helicobacter pylori o Bacteroides fragilis
Gram-negative pathogens and meningitis
o Neisseria meningitidis
o Some E. coli serotypes
o Haemophilus influenzae
Gram-negative pathogens in the urinary tract
o Some E. coli serotypes
o Proteus mirabilis
o Klebsiella pneumoniae
Gram-negative pathogens- STIs
o Neisseria gonorrhoeae
o Chlamydia trachomatis
o Treponema pallidum
Gram-negative pathogens in wound infections
o Some E. coli serotypes
o Bacteroides fragilis
o Pseudomonas aeruginosa
3 groups of worms
nematodes
trematodes
cestodes
nematodes
round worms
intestinal, larva migrans, tissue
trematodes
flatworms, flukes
blood, liver, lung, intestinal
cestodes
tapeworms
non-invasive, invasive
features of helminths
cannot usually reproduce without a period of development outside the body
although they usually produce a large number of larvae or eggs, they cannot increase the burden without re-exposure
pre-patent period
interval between infection and appearance of eggs in the stool
intestinal nematodes
transmitted from human to human via egg or larvae
the egg or larva is not usually infectious when first passed and has to undergo a period of development in the soil
Ascaris lumbricoides: the large roundworm
cream coloured
15-30cm long
lives a year or more
pre-patent period is 60-75 days
loeffler’s syndrome
associated with larval migration through lungs
10-14 days after infection
cough, fever, wheeze, eosinophilia
Ascaris lumbricoides effects of adult
often asymptomatic
can be mechanical e.g. intestinal obstruction or malnutrition
Ascaris lumbricoides odd presentation
emerging from nose
perforated eardrum
The Hookworm
white worm
1cm in length
life expectancy 1-5 years
The Hookworm 2 species
ancylostoma duodenale
necator americanus
The Hookworm clinical features
ground itch- papules at site of entry of the larvae
pulmonary symptoms- mild due to pulmonary migration
most common cause of iron deficiency
The Hookworm diagnosis
stool microscopy for eggs
The Hookworm treatment
iron supplements
pyrantel
mebendazole
Enterobius vermicularis: the pinworm or threadworm
most common helminth infection in the uk
Enterobius vermicularis life cycle
adult is resident in large bowel
female adult emerges from anus at night to lay eggs on the perineum
the eggs are infectious after 4 hours are ingested by next host
Enterobius vermicularis clinical features
pruritus ani
appendicitis
vaginal penetration- endometritis, infertility
affects whole families
Enterobius vermicularis diagnosis
microscopy of sellotape strip from perianal region
Enterobius vermicularis treatment
mebendazole
piperazine
pyrantel
Trichuris trichiura: the whipworm
2-5cm long
live 1 year
pre-patent period is 70-90 days
partially buried in the mucosa of large bowel
Trichuris trichiura clinical features
resident of large bowel
asymptomatic
co exists with ascaris lumbricoides
Trichuris trichiura diagnosis
stool microscopy for eggs
Trichuris trichiura treatment
mebendazole
albendazole
Strongyloides stercoralis
causes strongloidiasis
2mm long
lies buried in small intestinal mucosa
pre-patent period is 17-28 days
Strongyloides stercoralis clinical features
pruritus at site of entry
malabsorption
eosinophilia
hyperinfection syndrome
visceral larva migrans
caused by toxocara canis and t.cati (dog and cat roundworm)
mainly a disease of children
diagnose with eosinophilia and serology
treat with mebendazole
ocular toxocariasis
larvae trapped in retina see a granulomatous reaction blindness diagnose with serology and biopsy treat with mebendazole
cutaneous larva migrans
creeping itchy skin eruption
dog hookworms
lesions at site where larvae penetrate
treat with topical or systemic thiabendazole
Dracunculus medinensis: The Guinea worm
100cm long
lives one year subcutaneously
incubation period is one year
worm emerges from skin
Dracunculus medinensis clinical
localised pain
blister bursting
tetanus or sepsis
Dracunculus medinensis diagnosis
drop water on ulcer promotes egg release
Dracunculus medinensis treatment
local- wind out worm
mebendazole
Dracunculus medinensis prevention
sieving of water
Wuchereria bancroftii
causes elephantiasis
adults live in lymphatic system and survive 30 years
Wuchereria bancroftii diagnosis
demonstration of microfilaria in blood taken at right time of day (2300-0100)
Wuchereria bancroftii treatment
diethylcarbamazine
Trichinella spiralis
cause of trichinosis
Trichinella spiralis clinical picture
asymptomatic GI disturbance associated with worm development fever, headache, cough periorbital oedema myocarditis pneumonitis
Taenia saginatum
beef tapeworm
5-10metres long
pre-patent period is 12 weeks
Taenia saginatum clinical
asymptomatic
proglottids may emerge from anus
Taenia saginatum diagnosis
stools with eggs and proglottids
Taenia saginatum treatment
niclosamide
praziquantel
flukes
blood
liver
lung
bowel
all have snail as an intermediate host
schistosomiasis
adult fluke is 12cm long
life span is 3-5 years
schistosoma haematobium- africa, Arabia, Mauritius
schistosoma mansoni- africa
schistosoma japonicum- china, japan, phillippines
katayama fever
initial immune complex mediated illness 2-4 weeks after exposure eosinophilia diarrhoea cough hepatomegaly and splenomegaly
liver flukes
adults resident in human biliary tree
invade liver via biliary tree
opisthorcis filenius
the bovine liver fluke
lung flukes
resident in lung
paragonimus westermant
chinese lung fluke
intestinal flukes
desident in gut
fasciolopiasis
giant chinese gut fluke
intestinal flukes
desident in gut
fasciolopiasis
giant chinese gut fluke
m. tuberculosis
tubercolosis
m. kansasii
chronic lung infection
m. maranium
fish tank granuloma
m. ulcerans
buruli ulcer
m.leprae
leprosy
buruli ulcer formation
nodule small ulcer large ulcer deforming bone destruction (m. ulceran bacterium)
buruli ulcer treatment
antibiotics for 8 weeks
wound management
surgery
microbiology of mycobacteria
aerobic, non-spore forming, non-motile bacillus
cell wall= high molecular weight lipids
slow growing e.g. tb generation time is 15-20 hours
mycobacteria cell wall
weakly gram positive
survives inside macrophages
contains mycolic acids and lipoarabinomannan
mycobacterial slow growth
slow reproduction so slow growth in humans (slow onset of disease) and on agar
it responds slowly to treatment as well
mycobacteria acid fast bacilli
need this stain as the high lipid content in the walls make it gram resistant
ziehl-neelsen- carbol fuchsin, acid alcohol, methylene blue
mycobacterial slow growth in culture
first need decontamination steps to kill off other rapid growing bacteria
solid culture= egg based lowenstein jensen, microspoy positive material 2-4 weeks, negative 4-8 weeks
liquid culture= 1-3 weeks, automated systems BACTEC mycobacterial growth indicator tube
TB reactivation risk after exposure
risk = 10% lifetime risk, most in first 2 years then 0.1% a year
increased risk= young infants and elderly, malnutrition, intensity of exposure and immunosuppression
tuberculoid leprosy
associated with tissue hypersensitivity and granulomata
paucibacillary lesions with low numbers of mycobacteria
tissue damage e.g. nerves
predominate th1 biased cd4+ t cell responses- IFN-g and TNF-a production
leptromatous leprosy
lesions full of bacilli but little or poorly formed granulomata
extensive skin lesions
predominant th2 biased cd4+ t cell response- IL4,5,10 production
primary TB
bacilli taken into lymphatics to hilar lymph nodes
latent TB
cell mediated immune response from t-cells
primary infection is contained but immune response persists
no clinical disease but detectable immune response to TB on skin test
pulmonary tuberculosis
granuloma forms around -bacilli settle in the apex
- the apex has more air and less blood supply so fewer cells for immune response
- immune response and necrosis results in abscess of bacilli forming and caseous material coughed up leaving cavity
- can occur immediately or after latent TB
TB spreads beyond lungs
enters lymph nodes
genitourinary tb tb meningitis miliary tb pleural tb bone and joint tb
TB spreads beyond lungs
enters lymph nodes
genitourinary tb tb meningitis miliary tb pleural tb bone and joint tb
common viral infections
respiratory viruses rash causing viruses herpes group hepatitis group enteroviruses diarrhoea causing viruses HIV
diseases and viruses
same virus can cause different diseases e.g. enteroviruses cause resp infections and meningitis
different viruses can cause the same disease e.g. different hepatitis viruses
basic properties of viruses
only grow inside cells
possess only one type of nucleic acid
have an outer protein coat, some have a lipid envelope as well
essentially inert outside the host cell
are viruses living
have nucleic acid
have outer protein coat
can replicate once inside a living host cell and pass on its genetic code- using host enzymes
are viruses non- living
non cellular
no cell wall
cannot replicate by themselves
have no organelles
attachment (viral replication)
viral and cell receptors
viruses need specific receptors to attach to cells to enter them
this dictates the type of cells viruses can infect
cell entry (viral replication)
only central viral core carrying nucleic acid and some proteins enter the cell
interaction (viral replication)
using cell materials such as enzymes, amino acids and nucleotides
they replicate
subvert host cell defence mechanisms
replication (viral replication)
may localise in nucleus, cytoplasm or both
produce progeny viral nucleic acid and proteins
assembly (viral replication)
occurs in nucleus e.g. herpes virus or cytoplasm e.g. polio or at cell membrane e.g. influenza
release (viral replication)
via lysis of a cell or by exocytosis
viruses causing disease
- damage by destruction of host cells
- by modification of cell structure or function
- involving over-reactivity of the host as a response to infection
- damage through cell proliferation
pathogenesis of rotavirus
- following ingestion, rotaviruses infect epithelia cells of the small intestine
- there is shortening and atrophy of the villi and flattening of epithelia cells
- decreases surface area of small intestine and limits production of digestive enzymes
- they suffer malabsorption
- causes diarrhoea
infection with hepatitis B
majority are asymptomatic
there is a massive antibody and CTL response- destroying virally infected hepatocytes
can cause extensive liver damage
hepatitis B virus and chronic carrier state
- steady state between virus replication in host cells and host defence response
- limited by sustained viral replication
- hepatocyte regeneration
- no clinical symptoms
development of cervical carcinoma
- HPV types 16 and 18 infect suprabasal layer of genital system
- partial replication and gradual movement of cells to mucosal surface through natural wear and tear
- HPV genome is integrated into host cell chromosome
- viral gene expression by HPV E2 protein is lost and HPV E6 and E7 are expressed
- two cell growth and proliferation suppressor proteins are prevented from operating
- excessive cell growth and proliferation occurs and cervical cell carcinoma results
viral evasion at cellular level
latency: allows viruses to cause life threatening disease in the immunosuppressed
spreads cell to cell
viral evasion and molecular level
antigenic variability
prevention of host cell apoptosis
down regulation of interferon and other host cell defence proteins
interference with host cell antigen processing pathways
viral diagnosis
electron microscope
cell culture
antigen- viral protein detection
serology
viral treatment
treat with antivirals
prevent with vaccines
viral treatment
treat with antivirals
prevent with vaccines
fungi biology
eukaryotic chitinous cel wall exist as yeast or mould heterotrophic move by means of growth or spores
yeast vs mould
yeast= single celled organisms that divide by budding. small. <1% of fungal species
moulds= multicellular hyphae. form spores.
dimorphic fungi= switch between the two depending on the conditions
common fungal infections
nappy rash
athletes foot
fungal nail infection
fungal asthma
immunocompromised hosts and fungal disease
candida line infections
invasive aspergillosis
pneumocystis
mucormycosis
post surgical patients and fungal disease
intra abdominal infection
healthy host and fungal disease
fungal asthma
travel associated fungal infection
diagnosing fungi
microscopy and histology
culture
serology
mucosal candidiasis
thrush treat with topical antifungals and oral fluconazole associated with: - diabetes - immunocompromised - antibiotics - pregnancy
invasive aspergillosis and galactaomannan
chest focus more common
culture is insensitive
can cause brain disease
more common in immunocompromised
pneumocystis pneumonia
immunocompromised patients
unable to culture
treat with co-trimoxazole
treating fungal disease- selective toxicity
aims of drug is to achieve inhibitory levels of agent at the site without host cell toxicity
relies upon identifying molecules with selective toxicity:
- ones that dont exist in humans
- different to human analogue
- human cells recover from toxicity by alternative metabolic pathways
fungal cell targets- DNA/RNA and protein synthesis
similar to mammalian
drug e.g. fluctosine
fungal cell targets- cell wall
mannoproteins
B1,3 and 1,6 glucan
chitin
dont exist in humans
drug e.g. echinocandins
fungal cell targets- plasma membrane
ergosterol
human membrane contains cholesterol instead
drug e.g. amphotericin, azoles, terbinafine
ergosteol synthetic pathway
agents act early in pathway will be cidal
those acting at later stages will be fungistatic
allylamines
reversible inhibition of squalene epoxidase
fungicidal
absorbed well but extensive first metabolism so bioavailability is 45%
used to treat dermatophytes
azoles
dose dependent inhibitors of 14alpha-sterol demethylase
fungistatic
newer azoles have increase spectrum of activity
spectrum of activity of azoles
determined by degree of inhibition of 14alpha-sterol demethylase and secondary targets
azole adverse effects
relatively safe
drug interaction due to CYP450 metabolism
alopecia with long term fluconazole
30% on voriconazole suffer reversible visual disturbances
azole resistance
multiple mechanisms in candida:
target site modification
-increased expression of ERG11
-efflux
polyenes
- amphoteric molecules
- disruption caused by insertion of molecule into the membrane displaces and affects activity of membrane bound proteins
- forms pores so fungicidal
- 10x lower affinity for cholesterol but still can cause toxicity
echinocandins
inhibit 1,3 beta glucan synthase fingicidal to susceptible yeasts fungstatic to moulds with activity at hyphal tip IV only few side effects
echinocandins
inhibit 1,3 beta glucan synthase fingicidal to susceptible yeasts fungstatic to moulds with activity at hyphal tip IV only few side effects
protozoa
single cell with nucleus
>30,000 species
5 groups of protozoa
flagellates amoebae sporozoan ciliates microsporidia
flagellates
leishmaniasis
trichomonas vaginalis
giardiasis
amoebae
amoebiasis
sporozoan
cryptosporidiosis
toxoplasma gondii
malaria (plasmodium)
leishmaniasis
spread by bite of the sandfly
>20 species that affect humans
leishmaniasis clinical pictures
cutaneous= ulceration mucocutaneous= ulceration
both can cause social rejection and scarring
visceral= fever, weight loss, hepatomegaly, anaemia
thrichomonas vaginalis
sexually transmitted asymptomatic dysuria yellow frothy discharge treat with metronidazole
giardiasis
giardia lamblia faecal-oral spread diarrhoea cramps treat with metronidazole
amoebiasis
enteraemoeba histolytica faeco-oral spread dysentery liver and lung abscesses treat with metronidazole
cyrptosporidiosis
waterborne diarrhoea womiting oocytes seen in stool sever in immunocompromised
toxoplasmosis
ingestion of contaminated food and water
acute maternal infection can be fatal in pregnancy
toxoplasmosis can cause
disseminated disease
toxoplasma encephalitis
chorioretinitis
5 species of malaria
Plasmodium falciparum Plasmodium ovale Plasmodium vivax Plasmodium malariae Plasmodium knowlesi
test for malaria
blood film
symptoms of malaria
fever chills headache myalgia fatigue diarrhoea
signs of malaria
anaemia
jaundice
hepatosplenomegaly (big spleen and liver)
life cycle of malaria
- mosquito bites infected human and ingests plasmodium gametocytes
- the gametocytes are within midgut and undergo development- becomes sporozoites in salivary gland
- they’re injected into blood and infect human liver hepatocytes
- develop into schizont and bursts out and infects red blood cells
- this stage lasts 48 hours with haemolysis causing anaemia and jaundice
p. falciparum
-The pathophysiology of complicated malaria is mostly down to the infected RBCs ability to
adhere to endothelial cells
-RBCs infected with p. falciparum have proteinaceous knobs on the surface that bind to
endothelial cells in the vessels and other RBCs
-This can cause small vessels to become obstructed by clumps of red blood cells causing hypoxia of the tissues, microinfarcts in brain and lung
complicated cerebral malaria
vascular occlusion drowsiness raised intracranial pressure seizures coma
complicated malaria and acute respiratory distress
vascular occlusion anaemia lactic acidosis increased vascular permeability hypoxia pulmonary oedema
complicated malaria and renal failure
vascular occlusion
dehydration- hypotension
haemolysis- haemoglobulinuria
proteinuria
fatigue
haematuria
complicated malaria and bleeding
thrombocytopenia
activation of coagulation cascade
worsened anaemia
complicated malaria and shock
anaemia
bleeding
gram -ve sepsis
increased vascular permeability
hypotension
tachycardia
pale
malaria treatment
complicated= IV artesunate, IV quinine+doxycycline
supportive measures for malaria
cerebral= anti-epileptics ARD= oxygen, diuretics, ventilation renal failure= dialysis sepsis= antibiotics bleeding= blood products
malaria relapses
p.ovale and vivax can form hypnozoites in the liver- lying dormant
primiquine eliminates this
antibiotics
agents produced by microorganisms that kill or inhibit the growth of other microorganisms
antimicrobials
most agents currently used are semi-synthetic derivatives so = antimicrobials
antifungal, antibacterial, antihelminitic, antiprotozoal and antiviral
antibiotics as antibacterials
antibiotic tends to= antibacterial
bind to target site on bacteria
give time and support for the immune system to deal with an infection
antibiotics affecting bacterial cell wall synthesis
beta lactams= penicillins, cephalosporins, carbapenems, monobactams
glycopeptides= vancomycin and teicoplanin
beta lactam antibiotics
disrupt peptidoglycan production by binding covalently and irreversibly to PBPs
to do so it diffuses through the cell wall
cell wall is disrupted and lysis occurs
gram positive is more susceptible
antibiotics affecting bacterial nucleic acid synthesis
DNA gryase- quinolines
RNA polymeras- rifampin
antibiotics affecting bacterial protein synthesis
ribosome 30s subunit- tetracyclines, aminoglycosides
ribosome 50s subunit- macrolides, chloramphenicol
antibiotics affecting bacterial folate synthesis
sulphonamides
trimethoprim
bacteria and accidental damage
destroy phagocytes or cells in which bacteria replicate endotoxins exotoxins inflammation diarrhoea
bacteriostatic
prevents growth by preventing multiplication kill >90% in 18-24 hours inhibit protein synthesis, DNA replication or metabolism MBC to MIC ratio >4
bactericidal
kill bacteria
>99.9% killed in 18-24 hours
inhibit cell wall synthesis
minimum inhibitory concentration
concentration required to stop bacteria from multiplying
lowest MIC does not equal best antibiotic
drugs must attach to binding site and occupy an adequate number of binding sites
to work effectively they should remain on binding site for a sufficient period in order for metabolic processes to be inhibited
concentration dependent killing
key parameter is how high the concentration is above MIC
time dependent killing
key parameter is the time the serum concentrations remain above the MIC during dosing interval
antibiotic considerations
release and absorption
distribution to site
half life and elimination
other antibiotic considerations
are they safe side effects renal function liver function pregnancy drug interactions
changing antibiotic target site
bacteria changes molecular configuration of binding site or masks it
destroying the antibiotic
e.g. beta lactam ring of penicillin is hydrolysed by bacterial enzyme beta lactamase
preventing antibiotic access
modify bacterial membrane porin channel size, numbers and selectivity
removing bacteria from bacteria
proteins in bacterial membranes act as an export or efflux pumps- so antibiotic levels are reduced
intrinsic resistance
subpopulations of a species will be equally resistant
acquired resistance
bacterium that was previously susceptible obtains ability to resist the activity of an antibiotic
MRSA
staphylococcal cassette chromosome mec, contains resistance gene
VRE
plasmid mediated acquisition of gene encoding altered amino acid on peptide chain preventing vancomycin binding
ESBL
mutation at the active site extended range of antimicrobial resistance to form extended spectrum beta lactamase (ESBL) inhibition
plasmid spread resistance
AmpC b-lactamase resistance
broad spectrum penicillin, cephalosporin resistance
encoded on the chromosome in bacteria
beta lactams
group of drugs that contain beta lactam ring- detroy cell walls
penicillin V, amoxicillin, cephalexin
cephalosporins
beta lactams
good for penicillin allergy
better for resistance bacteria
gram positive antibiotics
thick cell wall so need simple cell wall weapon
gram negative antibiotics
thin cell wall so need a different weapon
methicillin resistant staphylococcus aureus
describes all staph that are resistant to beta lactams
macrolides
clarithromycin and erythromycin
for gram positives and atypical pneumonia pathogens
use in penicillin allergy and severe pneumonia
linosamides
clindamycin
gram positives e.g. s. aureus
use for cellulitis or necrotising fasciitis
tetracyclines
doxycycline
broad spectrum but mainly gram positive
use for cellulitis if penicillin allergy and chest infections
quinolones
ciprofloxacin
for gram negatives
urinary tract infections, gall bladder infections, abdominal infections
beta lactams for gram negative
amoxicillin- clavulante, cefuroxime, meropenem, ceftriaxone
beta lactams for gram negative
amoxicillin- clavulante, cefuroxime, meropenem, ceftriaxone
HIV genome
codes for 9 genes Gag Pol Env Tat Nef Vif Vpr Vpu Rev
prevention strategies for HIV
HIV testing early diagnosis sti testing HAART screening of blood products microbicides male circumcision post-exposure prophylaxis Pre-exposure prophylaxis behavioural prevention strategies for HIV future
features that make HIV successful
transmitted by sexual intercourse
latency so individuals don’t know they’re spreading the disease
stops immune system functioning
ineffective at replication so mutates every time
HIV origins
HIV-1 = transmission of simian immunodeficiency virus (SIV cpz) from chimps to humans
HIV-2 = arose from SIV sm
HIV types
Main, outlying and new groups
main separated into A-D, F-H, J-K
HIV replication
- attachment via gp120 to CD4 receptors
- entry
- uncoating
- reverse transcription -error prone
- genome integration by integrase enzyme
- transcription of viral RNA
- splicing of mRNA and translation into proteins
- assembly
- budding
HIV receptors
their glycoprotein- gp120 binds to human CD4 receptors
HIV genes: Pol
encodes reverse transcriptase, integrase, protease
HIV genes: Env
encodes envelope proteins
HIV genes: Nef
increases infectivity
HIV genes: Tat
contributes to viral replication
HIV genes: Gag
encodes structural proteins
HIV genes: Rev
binds to viral RNA and allows export from nucleus and regulates RNA splicing
cell tropism- infected cells in HIV
CD4 cells macrophages dendritic cells CD34 bone marrow progenitors astrocytes
initial HIV infection
- virus enters via mucosa (vaginal, rectal etc.)
- local infection within mucosal macrophage then spreads to other cells
- as these are APCs they will migrate to local lymph nodes and T cells
- infection spills into blood stream
mechanism for CD4+ T cell depletion
direct cytotoxicity of infected cells
activation induced death
decreased production due to infected progenitors in bone marrow
immune system consequences of HIV
decreased number and function of CD4 t lymphocytes
excessive activation of immune system
decreased proliferation in response to antigens
decreased macrophage function
sanctuary sites for HIV
genital tract
CNS
GI tract
bone marrow
reservoir cells for HIV
macrophages
T cells
microglia
UNAIDS 90/90/90 goals
90% of people with HIV diagnosed
90% of diagnosed on ART
90% viral suppression for those on ART by 2020
HIV transmission routes
blood
sexual
vertical- mother to child
post-exposure prophylaxis
PEP
treatment commences within 72 hours of exposure
continued for one month
Pre-exposure prophylaxis
PrEP
good evidence for effectiveness
ongoing trial in the UK to address questions such as duration of dose
behavioural prevention strategies for HIV
sex education
avoid concomitant sexual partners
reduce high risk sexual partners
consistent condom use
future prevention strategies for HIV
vaccines
benefits of knowing HIV status
access to appropriate treatment
reduction on mortality
reduction in vertical transmission
reduction of sexual transmission
high risk behaviours of HIV
sex with people from high prevalence groups e.g. subsaharan africa and thailand etc.
multiple sexual partners
rape in high prevalence localities
consider HIV if recurring conditions, e.g.
shingles oral candidiasis flu like symptoms rash unexplained weight loss/ diarrhoea unexplained lymphadenopathy
screening tests for HIV
p24 antigen test
test at 4 weeks, if negative repeat at 8 weeks if high suspicion
managing the result of HIV
negative- repeat if within window
positive-arrange appointment within 48 hours, explain test is reactive and needs further investigation
partner notification and HIV
discuss with all HIV infected people
length of look back depends on circumstances
encourage them to inform their partners or agree to notification
document discussion
discuss consequences of reckless transmission
criminalisation of HIV
only those who know their status are criminally liable
confidentiality definition
Right of an individual to have personal, identifiable medical information kept private. Such information should be available only to the physician of record and other health care and
insurance personnel as necessary
confidentiality and HIV
allows disclosure to known sexual partner if at risk and unaware
must inform patient you are doing so unless it endangers the contact
don’t reveal identity of patient
markers of HIV
CD4 count
HIV viral load
seroconversion
period of time during which HIV antibodies develop and become detectable
acute HIV syndrome
usually takes 2-4 weeks
similar to glandular fever or flu
can present with opportunistic infections
non-specific symptoms
HIV clinical latency
undiagnosed- the immune system takes control and CD4 increases
overtime CD4 does begin to decline
can then present with more opportunistic infections
development of HIV symptoms
shingles
candida
oral hairy leukoplakia
recurring infections
acquired immune deficiency syndrome
AIDs
CD4<200 and/or AIDs defining illness present
AIDS defining illnesses
pneumocystis pneumonia
other respiratory infections
TB
pneumocystis pneumonia
most common AIDS defining illness
most common opportunistic infection
symptoms of pneumocystis pneumonia
fevers
dry cough
chest pain
drop in O2 sats
tests for pneumocystis pneumonia
chest xray- can be normal
ABG test for hypoxia
induced sputum
treatment of pneumocystis pneumonia
antibiotics- co-trimoxazole
and steroids
HIV clinical latency
undiagnosed- the immune system takes control and CD4 increases
overtime CD4 does begin to decline
can then present with more opportunistic infections
development of HIV symptoms
shingles
candida
oral hairy leukoplakia
recurring infections
acquired immune deficiency syndrome
AIDs
CD4<200 and/or AIDs defining illness present
AIDS defining illnesses
pneumocystis pneumonia
other respiratory infections
TB
pneumocystis pneumonia
most common AIDS defining illness
most common opportunistic infection
symptoms of pneumocystis pneumonia
fevers
dry cough
chest pain
drop in O2 sats
tests for pneumocystis pneumonia
chest xray- can be normal
ABG test for hypoxia
induced sputum
treatment of pneumocystis pneumonia
antibiotics- co-trimoxazole
and steroids
TB and HIV
can present at any CD4 count
atypical presentations with lower CD4 count
all patients with TB should be tested for HIV
CNS presentations of HIV
toxoplasmosis- reactivation of latent infection
meningitis- higher incidence and mortality in HIV
cancers and HIV
increase in any cancer associated with a virus
HepB/B- hepatocellular carcinoma
human papilloma virus- cervical cancer
herpes 8- kaposi’s sarcoma
kaposi’s sarcoma
single to multiple lesions
on the skin, mouth, respiratory tract, GI tract
late diagnosis of HIV
increased transmission
increased morbidity
increased mortality
highly active antiretroviral therapy
HAART
3+ antiretroviral drugs
act on different points in HIV replication cycle
aim to reduce viral loads to undetectable levels- not a cure
how do antiretroviral drugs function
fusion/entry inhibitors
reverse transcriptase inhibitors
integrase inhibitors
protease inhibitors
HIV resistance
1 mutation in every 2 new viruses produced
develop drug resistance through:
non-adherence (missing one or two doses)
drug-drug interactions
avoiding HIV resistance
good drug adherence
checking drug interactions
groups at risk of HIV
men who have sex with men heterosexual women injecting drug users commercial sex workers heterosexual men truck drivers migrant workers
problems for antiretroviral treatment in developing countries
awareness procurement/delivery clinical services cost adherence efficacy co-morbidities
