Pathogenic Organisms Flashcards
Features of bacteria
> cause infectious disease
single-cell
prokaryotes
reproduce by binary fission
have peptidoglycan cell walls
Importance of gram staining
1) classification of bacterial species
2) identification of the type of bacteria causing an infection
3) guides the antibiotic class to be used in eradicating bacterial infection
Classification of gram positive bacteria
1) aerobic
> cocci e.g., streptococci and staphylococci species
> bacilli e.g., bacillus, cornyebacterium species
2) anaerobic
> cocci e.g., streptococci species
> bacilli e.g., clostridium species
Commonest gram positive bacteria
1) streptococcus pneumoniae (cocci)
> pneumonia
> meningitis
> septicaemia
2) staphylococcus aureus (cocci)
> soft tissue infections
> boils
> septicaemia
> food poisoning
> MRSA
3) staphylococcus pyogenes (cocci)
> sore throat
> cellulitis
> necrotising fasciitis
4) clostridium difficile (bacilli)
> diarrhoea
> pseudomembranous colitis
Test for staphylococci bacteria
coagulase test
Features of Staphylococci Aureus infections
> commensal organism on skin
causes boils, soft tissue infections, septicaemia, food poisoning, MRSA
coagulase test positive
resistant to penicillin due to beta-lactamase
Features of alpha-haemolytic streptococci
> turns blood agar green in laboratory
streptococcus pneumoniae, viridans etc
s.pneumonia causes pneumonia, meningitis, septicaemia
s.viridans causes infective endocarditis
Features of beta-haemolytic streptococci
> turns blood agar clear in laboratory
grouped from A>G
groups A, B and D are clinically most important
group A s. pyogenes causes sore throat, cellulitis, necrotising fasciitis
group B s. agalactiae causes neonatal sepsis, meningitis, bacteraemia
group D enterococcus faecalis, faecium cause urinary tract infections
Features of Clostridium Difficile
> gram positive bacilli
difficult to culture
carried asymptomatically in the gut of healthy people
causes diarrhoea due to toxin production which can be fatal
increased risk if antibiotic use increased which disrupts the normal gut flora
causes pseudomembranous colitis
spreads by spores
detected by stool sampling using ELISA antigen/toxin testing
Features of Clostridium Perfringens
> gram positive bacilli
found in soil and human/animal gut/faeces
causes food poisoning if food is contaminated with it
Features of Clostridium Tetani
> causes tetanus by producing toxins
results in muscle spasm due to loss of inhibition at the neuromuscular junction
an antigen modified toxin is used to immunise against tetanus
Classification of Gram Negative bacteria
1) aerobic (strict)
> bacilli e.g., legionella
2) aerobic
> cocci e.g., neisseria gonorrhoeae and meningitidis
> bacilli e.g., bordetella pertussis and haemophilus influenzae and salmonella and e.coli
3) microaerophilic
> bacilli e.g., campylobacter and helicobacter
4) anaerobic (strict)
> cocci
> bacilli e.g., bacteriodes
Features of Neisseria Species
> causes meningitis (N. Meningitidis/Meningococcus)
isolated from a sterile site e.g., blood cultures or CSF
PCR test available
life threatening
> causes gonorrhoea (N. Gonorrhoeae)
causes urethritis in men
causes pelvic inflammatory disease in females
spread by sexual contact
Features of E.Coli
> humans and animals are reservoirs of the bacteria
produces endotoxins and exotoxins
ferments lactose
causes UTI
causes traveller’s diarrhoea
causes bloody diarrhoea
causes haemolytic uraemic syndrome
Features of salmonella
> doesn’t ferment lactose
self-limiting enterocolitis with/without blood diarrhoea
2nd most common cause of bloody diarrhoea
causes typhoid fever
isolated from blood cultures and faeces
vaccination available for foreign travel
