Systemic Microbiology Flashcards
List some of types of microbe.
Viruses Prions Protozoa Fungi Bacteria Helminths
Name some of the common relationships between host and microbiota/
Symbiosis
Commensals
Parasites
Mutualism
Breifly describe the differences between a Eukaryote and a Prokaryote.
Prokaryote has a nucleoid, a capsule a cell wall and a flagellum
Eukaryote has a membran-enclosed nucleus, a nucleolus, and mitochonria
They both have ribosomes and a cell membrane
What is taxonomy?
Classification of organisms
Organisms are identified by two names, indicating what?
The genus and the species
- e.g. Staphylococcus aureus
- Streptococcus pyogenes
- Pseudomonas aerugiosa
Describe gram staining.
Widely used stain Separates bacteria into two groups - gram negative - gram positive Also allows the shape of the bacteria to be identified
Which gram group has a thicker cell wall?
Gram positive (doesn’t have periplasm or an outer membrane)
What colour are gram negative and gram positive bacteria stained?
Positive - purple
Negative - pink
Describe two exceptions on gram stain.
Mycoplasma doesn’t stain as it doesn’t have a cell wall. They are also weakly gram positive but stain best with an acid-fast stain
Spirochetes have a gram negative wall but are too small to be seen with a light microscope
What are the different groupings of cocci bacteria?
Coccus - single round bacteria Diplococci Encapsulated diplococci Staphylococci - pyramid Streptococci - long chain Sarcina - cube Tetrad - group of four
What are the different groupings of bacilli bacteria?
Coccobacillus - oval Bacillus - single bacteria Diplobacilli Paslisades - joined on the long side Streptobacilli - long chain
What are some different groupings of non cocci or bacilli bacteria?
Enlarged rod Vibrio - kidney shape Comma's form Club rod Helical form Corkscrew's form Filamentous Spirochete
Give some examples of gram positive bacilli.
Clostridia
Bacillus
Listeria
Give some examples of gram negative bacilli.
E.Coli Klebsiella Pseudomonas Salmonella Shigella
Give an example of a gram negative cocci.
Neisseriae
List the four classifications of growth atmosphere for bacteria.
Obligate aerobes
Facultative anaerobes
Microaerophilic bacteria
Anaerobes
What are endospores?
Metabolically dormant forms of bacteria that are more resistant to disinfectants, drying or heating
When do bacteria form endospores?
When there is a shortage of needed nutrients - can lie dormant for years
Becomes active again when exposed to favourable environment
Which bacteria genres can form endospores?
Bacillus and Clostridium
What are the 5 types of classification of bacteria?
1) Gram Stain
2) Shape
3) Growth Atmosphere
4) Endospores
5) DNA sequencing
Describe the structure of a basic bacteria?
Cell envelope Cytoplasmic membrane Cell wall (gram negatives have an outer membrane of LPS called endotoxin and a periplasm) Capsule Flagella Pili/Fimbriae
List the four main ways bacteria can be pathological.
Toxins
Adhesions
Enzymes
Capsules
How do bacteria reproduce and adapt?
They reproduce by binary fission - this allows alteration of genetic material which enables adaptation
What are three of the methods of gene transfer?
Transformation
Transduction
Conjugation
What are the non-specific immune defences of a host against bacteria?
External biochemical and mechanical barriers
Phagocytic cells, complement and NK cells
What are the specific immune defences of a host against bacteria?
Recognition of antigens and production of immune factors
What host factors increases their susceptibility to infection?
Immunosuppression
Asplenia
Breaches in physical barriers - wounds, medical devices (CVL, urinary catheter and ETT)
What are the two routes of infection?
Endogenous Exogenous - person to person - food/water/airborne - vector borne - fomites
How are bacteria directly and indirectly diagnosed in the laboratory?
Indirect - antibodies Direct - microscopy - culture - antigen detection - DNA detection - MALDI-TOF
What is the aerobic gram positive cocci bacteria that forms in clusters?
Staphylococcus
- catalase positive
What are the aerobic gram positive cocci bacteria that forms in chains?
Streptococcus and Enterococcus
- catalase negative
Name three staphylococci species.
- say whether than are coagulase positive or negative
S.aureus - coagulase positive
S.epidermidis - coagulase negative
S.saprophyticus - coagulase negative
What infection does S.saprophyticus commonly cause?
UTIs in women
What infections do S.aureus commonly cause?
Pneuomonia Cellulitis Septic arthritis Infective endocarditis Line associated infection
Name three diseases caused by exotoxin release
Toxic shock syndrome (TSST-1)
Scalded skin syndrome (exfoliatin toxin)
Food poisoning (enterotoxin)
How are the different types of streptococci described?
According to haemolytic activity
- beta haemolytic strep
- alpha haemolytic strep
What are the Lancefield groupings of Beta haemolytic strep?
A (strep pyogenes)
B (strep agaloactiae)
C
G
What kind of infections can group A streptococcus cause?
Non-invasive infections such as pharyngitis, scarlet fever and skin/soft tissue infections.
Invasive infections such as strep toxic shock syndrome, necrotising fasciitis and bacteraemia
What are virulence factors?
Molecules produced by pathogens (including bacteria)
What are the virulence factors of Group A streptococcus?
Fimbriae/pili M protein Haemolysins Exotoxins - streptokinase - hyaluronidase - strep pyrogenic exotoxin (Super antigen leading to massive release of cytotkines)
What is delayed antibody-mediated disease?
Diseases caused by group A streptococcus
- Rhuematic fever (fever, myocarditis, arthritis, chorea, nodules, erythema marginatum)
- Acute post-strep glomerulonephritis
What group is the leading cause of neonatal infection?
Group B Streptococcus
- colonisation in 10-40% of women
What can group B strep infections cause in adults?
Pneumonia Cellulitis Bone infection UTI Bacteraemia Endocarditis
Which strep haemolytic is streptococcus pneumonia classified as?
Alpha haemolytic
- gram positive diplococci
What are the risk factors for a strep pneumoniae infection?
Asplenia
Co-morbidities
Viral infection may be a precursor for pneumonia
Immune deficiencies
What infections does strep pneumoniae most commonly cause?
Pneumonia in adults
Otitis media in children
Bacterial meningitis in adults
What are some of the viridans streptococci?
- alpha haemolytic strep
S.Sangius
S.Mutans
S.Mitis
S.Salivarus
Which bacteria group are commensals of the upper respiratory and GI tract, with few virulence factors and are associated with dental caries?
Viridans streptococci
- a cause of bacterial endocarditis
Which strep group is a frequent cause of abscesses in the abdominal cavity, chest and brain?
Strep milleri group
- includes strep anginosus, S.constellatus and S.intermedius
Which haemolytic group does strep milleri belong to?
Often alpha haemolytic, but can be beta or non-haemolytic
Which Lancefield group antigen does Enterococcus carry?
Group D antigen
Which infections do entercocci commonly cause?
UTIs, endocarditis, biliary tract and abdominal infections
Gram positive bacilli can be split into spore forming and non-spore forming. Name some examples of each.
Spore forming - Bacillus - Clostridium Non-spore forming - Corynebacterium - Listeria
Describe bacillus species bacteria.
Large chain gram positive bacilli
Aerobic
Human pathogens include B.anthracis and B.cereus
Describe Bacillus anthracis.
Cutaneous/inhalational/GI infection
Capsulated
Medusa head appearance
Exotoxin - oedema factor, protective antigen, lethal factor
Describe the B.cereus bacteria.
Causes food poisoning
They are heart resistant spores that produce enterotoxins.
Breifly describe the Clostridium class.
Spore forming, gram positive bacilli
Anaerobic
What are the common infections caused by Clostridium infections?
Botulism
Tetanus
Gas Gangrene
Pseudomembranous colitis
Describe the what happens in the body when you get a C.botulinum infection.
Toxin binds to presynaptic nerve endings.
This blocks ACh release, causing descending flaccid paralysis
Describe the what happens in the body when you get a C.tetani infection.
This is a terminal spore (drumstick appearance)
The toxin here prevents release of inhibitory neurotransmitters leasing to sustained tetanic contraction
- e.g. lockjaw
Describe the pathogenic effects of gas gangrene (C.perfingens, C.novyi and C.septicum)
Clostridium myonecrosis
Rapidly spreading oedema, myositis, tissue necrosis and toxaemia
What problems/infections does C.difficilie cause?
Antibitoic associated diarrhoea
Pseudomembranous colitis
Describe Listeria monocytogenes.
Non-spore forming gram positive rods Exhibit beta haemolysis Has an endotoxin Usually transmitted by food Grows over a wide range of temperatures, including refrigeration
In what classes of patients is Listeria particularly important.
Pregnant women - risk of foetal infection
Neonates - maculopapular rash
Immunocompromised patients
Elderly patients
Describe Corynebacterium diptheriae (diptheria).
Gram positive rods in angular or palisade arrangements
Almost eradicated worldwide due to vaccinations
Describe the mechanism of action of Corynebacterium diptheriae.
It causes respiratory infection, with toxin production, which leads to pseudomembrane formation and associated swelling and obstruction
What are the clinical manifestations of Corynebacterium diptheriae
Bull neck
Pseudomembrane
Give some examples of gram negative diplococci
Neisseria (e.g. N.meningitidis and N.gonorrhoea)
Moraxella
What is special about the Moraxella bacteria?
It is a normal respiratory flora, that occasionally causes infection
Which diseases can Neisseria meningitidis cause?
Meningococcal disease
- meningitis
- bacteraemia
What are the virulence factors of Neisseria meningitidis?
Capsule (Serotypes A, B and C usually cause meningitis)
Endotoxin (causes vascular necrosis and haemorrhage into skin causing classical rash)
IgA1 protease
Which Neisseria meningitidis caspsuel serotypes can be vaccinated against?
Vaccine for A and C are available
What infections does Neisseria gonorrhoea cause?
STI - urethritis in men
PID in women
Septic arthritis/bacteraemia
Opthalmia neonatorum
Name some Enterobacteriacae gram negative bacilli.
E.Coli Enterobacter Klebsiella Proteus Serratia Shigella Salmonella
Which of the gram negative bacilli are lactose fermenting coliforms?
E.Coli
Enterobacter
Klebsiella
Which of the gram negative bacilli are non-lactose fermenting coliforms?
Serratia
Proteus
Salmonella
Shigella
What infections does E.Coli (a commensal of the intestinal tract) cause?
UTIs- commonly
Pneumonia, intra-abdominal infection, bacteraemia (most common bacteraemia) and meningitis in neonates
Which bacteria is the most common cause of gram negative bacteraemia?
E.Coli
What are the types of Enteropatogenic E.Coli?
Entertoxigenic E.Coli
Enteropathogenic E.Coli
Verocytotoxin producing E.Coli (VTEC)
What illness does Enterotoxigenic E.Coli produce?
Produces cholera like illness
What illness does Enteropathogenic E.Coli produce?
Produces infantile gastroenteritis
What illness does Verocytotoxin producing E.Coli produce?
E.Coli 0157 can lead to HUS and TTP
What infection can the normal intestinal flora bacteria of Klebsiella, Enterobacter and Serratia cause?
Pneumonia
UTIs
Wound infections
Describe the Proteus bacteria.
This is a non-lactose fermenter, highly motile bacteria that moves in swarms.
A common cause of UTI infections
Describe Salmonella bacteria.
This is a non-lactose fermenter, non-capsulated (except S.typhi) bacteria that is not a normal inhabitant of the gut.
It has over 2000 antigenic types
What kind of infections can Salmonella bacteria cause?
Diarrhoeal disease
S.typhi and S.paratyphi can cause typhoid
If the patient has sickle cell anaemia, they have an increased risk of an osteomyelitis infection
Describe the Shigella bacteria.
This is a non-lactose fermenter with a very low infective dose (10-100 organisms)
What are some of the types of the Shigella bacteria?
S.Sonnei (causes mild disease), S.Boydii, S.Dysenteriae (exotoxin) and S.Flexneri
What infections can the Shigella bacteria cause?
Gasteroenteritis with fever, cramps, diarrhoea (blood and mucous)
Name some non-Enterobacteriacae gram negative bacilli.
Pseudomonas aeurginosa
Burkholderia cepacia
Stenotrophomonas maltophilia
Acinetobacter species
Describe Pseudomonas aeurginosa.
Strict aerobes
Normal commensals of the GI tract
Can colonise in other sites (e.g. leg ulcers)
Can cause infections in burns patients, CF, bronchiectasis and UTIs
Often treated with multiple antibiotic
Describe Burkholderia cepacia.
This is a significant pathogen in Cystic Fibrosis patients.
Describe Stenotrophomonas maltophilia.
This is often a cause of hospital acquired infections as they are an antibiotic resistant organism.
Describe the Acinetobacter species.
Survive well in the environment and can be multiply resistant.
Describe Haemophilus influenzae (a gram negative cocco-bacilli).
Can be encapsulated.
Less common due to vaccinations
What infections does Haemophilus influenzae commonly cause?
Commonly causes LRTIs and Otitis media
H.influenzae type B is a major human pathogen causing epiglottitis and meningitis
Describe Legionella pneumophilia.
An atypical pneumonia.
Slow growing, requiring special media (found in water systems - transmission through aerosolisation of contaminated water)
Urinary Ag used in diagnosis
Serology is also useful
List some curved gram negative rods.
Campylobacter
Helicobacter
Vibrio Cholerae
Describe how Campylobacter and V.Cholerae are spread and the infections they cause.
Campylobacter - foodborne pathogen causing cramping, abdominal pain and bloody diarrhoea
V.Cholerae - contaminated water pathogen, causing watery diarrhoea and rice-water stools
Name some Spirochaetes and the infections they cause.
Treponema pallidum - causes Syphilis
Borrelia burgdorferi - lyme disease
Leptospira - Leptospirosis
