Microbiology - GI infections Flashcards
what is gastroenteritis?
- rapid onset diarrhoeal illness
- last <2 weeks
- with diarrhoea (loose or unformed stool) >3/ day or >200g of stool
- either viral or bacterial in aetiology
what is diarrhoea?
loose or watery stoool
>=3 times in 24 hours
acute/chronic /persistent
acute/chronic /persistent diarrhoea time limits
acute <14 days (may be bacterial or viral)
persistent 14-29 dats
chronic >30 days (parasites/non-infectious aetiology)
how is small bowel diarrhoea characterised?
- watery
- crampy abdo pain
- bloating and gas
- inflammatory cells rare
how is large bowel diarrhoea characterised?
- small volume
- painful
- occur with blood/mucous
- inflammatory cells common
what are the risk factors for gastroenteritis?
- food borne
- exposure related (outbreak, travel history, occupational, health care related, animal contacts, reptile contact, childcare facility)
- host related (young children/elderly, immunosuppressed, MSM, anal-gential, oral-anal, haemochromatosis)
what are the reportable organisms?
underreporting of GI infections (most self limiting) Reportable: - campylobacter - salmonella - shigella - E. coli 0157 - listeria - norovirus
what are the 3 mechanisms of disease?
- secretory diarrhoea (from toxin production)
- inflammatory diarrhoea
- enteric fever
give 2 examples of secretory diarrhoea
- cholera toxin
2. superantigens
how does the cholera toxin work?
- subunit procution
- cAMP opens Cl- channels at apical membrane of enterocytes
- causes efflux of Cl- to lumen with loss of water and electrolytes
- profound dehydration
how do superantigens work?
- superantigens bind directly to TCRs and MHC molecules
- massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response)
- secretory diarrhoea
what are the different ways you can diagnose GI infections?
- stool testing (cultures, PCR etc)
- enteric fever (blood and stool tested)
- parasites (stools for MS&C)
which bugs cause these extra-intestinal manifestations?
- aortitis
- osteomyelitis
- deep tissue infection
- salmonella
- yersinia
which bugs cause these extra-intestinal manifestations?
- haemolytic anaemia
- campylobacter
- yersinia
which bugs cause these extra-intestinal manifestations?
- glomerulonephritis
- shigella
- campylobacter
- yersinia
which bugs cause these extra-intestinal manifestations?
- HUS
- STEC
- shigella
which bugs cause these extra-intestinal manifestations?
- erythema nodosum
- yersinia
- campylobacter
- salmonella
- shigella
which bugs cause these extra-intestinal manifestations?
- reactive arthritis
- salmonella
- shigella
- campylobacter
- yersinia
which bugs cause these extra-intestinal manifestations?
- meningitis
- listeria
- salmonella
describe staph aureus
- catalase and coagulase +ve
- gram +ve coccus
how does staph aureus cause diarrhoea?
- superantigen
- produces enterotoxin that acts as a superantigen in GI tract
- releases IL1 and IL2
- causes prominent vomiting and watery non bloody diarrhoea
- self limiting
describe bacillus cereus
gram +ve rod spores
how do you get bacillus cereus?
- spores germinate in reheated fried rice
- heat stable emetic toxin (not destroyed by reheating/ if food not heated to high enough temp)
what does bacillus cereus infection cause?
- watery non-bloody diarrhoea
- self limiting
- rare cause of bacteraemia in vulberable population
- can cause cerebral abscess
