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
what is clostridia? 3 types?
- gram +ve anaerobe
- clostridium botulinum
- clostridium pefringens
- clostridium difficle
what is the source of clostridium botulinum?
- canned or vacuum-packed foods
- ingestion of preformed toxin (inactivated by cooking)
how does clostridium botulinum cause botulisism? tx?
- blocks ACh release from peripheral nerve synapses = paralysis
- treatment with antitoxin
what does clostridium pefringens cause? source?
food poisoning (watery diarrhoea, cramps, vomiting lasting 24 hours) source: reheated food (meat) incubation = 8-16 hours
what are the 2 toxins clostridium difficile produces?
pseudomembranous colitis
- Toxin A: enterotoxin = inflammation
- Toxin B = cytotoxin = virulence factor (more dangerous than A)
which antibiotics are responsible for antibiotic related colitis?
- cephalosporins
- cipro
- clindamycin
Tx: PO vancomycin
describe listeria monocytogenes
- beta haemolytic
- aesculin positive
- tumbling-weed motility
source of listeria monocytogenes
refrigerated food
unpasteurized dairy
vegetabloes
(grows at 4 degrees)
what are the symptoms of listeria monocytogenes
watery diarrhoea cramps headache fever little vomiting
who are at risk for listeria monocytogenes
perinatal infection
immunocompromised patients
elderly
BAD for pregnant women
tx for listeria monocytogenes
ampicillin
ceftriaxone
cotrimoxazole
