Microbiology - GI infections

Question 1

what is gastroenteritis?

Answer 1

• 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

Question 2

what is diarrhoea?

Answer 2

loose or watery stoool
>=3 times in 24 hours
acute/chronic /persistent

Question 3

acute/chronic /persistent diarrhoea time limits

Answer 3

acute <14 days (may be bacterial or viral)
persistent 14-29 dats
chronic >30 days (parasites/non-infectious aetiology)

Question 4

how is small bowel diarrhoea characterised?

Answer 4

• watery
• crampy abdo pain
• bloating and gas
• inflammatory cells rare

Question 5

how is large bowel diarrhoea characterised?

Answer 5

• small volume
• painful
• occur with blood/mucous
• inflammatory cells common

Question 6

what are the risk factors for gastroenteritis?

Answer 6

• 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)

Question 7

what are the reportable organisms?

Answer 7

underreporting of GI infections (most self limiting)
Reportable:
- campylobacter
- salmonella
- shigella
- E. coli 0157
- listeria
- norovirus

Question 8

what are the 3 mechanisms of disease?

Answer 8

1. secretory diarrhoea (from toxin production)
2. inflammatory diarrhoea
3. enteric fever

Question 9

give 2 examples of secretory diarrhoea

Answer 9

1. cholera toxin

2. superantigens

Question 10

how does the cholera toxin work?

Answer 10

• 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

Question 11

how do superantigens work?

Answer 11

• superantigens bind directly to TCRs and MHC molecules
• massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response)
• secretory diarrhoea

Question 12

what are the different ways you can diagnose GI infections?

Answer 12

• stool testing (cultures, PCR etc)
• enteric fever (blood and stool tested)
• parasites (stools for MS&C)

Question 13

which bugs cause these extra-intestinal manifestations?

• aortitis
• osteomyelitis
• deep tissue infection

Answer 13

• salmonella

- yersinia

Question 14

which bugs cause these extra-intestinal manifestations?

- haemolytic anaemia

Answer 14

• campylobacter

- yersinia

Question 15

which bugs cause these extra-intestinal manifestations?

- glomerulonephritis

Answer 15

• shigella
• campylobacter
• yersinia

Question 16

which bugs cause these extra-intestinal manifestations?

- HUS

Answer 16

• STEC

- shigella

Question 17

which bugs cause these extra-intestinal manifestations?

- erythema nodosum

Answer 17

• yersinia
• campylobacter
• salmonella
• shigella

Question 18

which bugs cause these extra-intestinal manifestations?

- reactive arthritis

Answer 18

• salmonella
• shigella
• campylobacter
• yersinia

Question 19

which bugs cause these extra-intestinal manifestations?

- meningitis

Answer 19

• listeria

- salmonella

Question 20

describe staph aureus

Answer 20

• catalase and coagulase +ve

- gram +ve coccus

Question 21

how does staph aureus cause diarrhoea?

Answer 21

• 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

Question 22

describe bacillus cereus

Answer 22

gram +ve rod spores

Question 23

how do you get bacillus cereus?

Answer 23

• spores germinate in reheated fried rice

- heat stable emetic toxin (not destroyed by reheating/ if food not heated to high enough temp)

Question 24

what does bacillus cereus infection cause?

Answer 24

• watery non-bloody diarrhoea
• self limiting
• rare cause of bacteraemia in vulberable population
• can cause cerebral abscess

Question 25

what is clostridia? 3 types?

Answer 25

• gram +ve anaerobe
• clostridium botulinum
• clostridium pefringens
• clostridium difficle

Question 26

what is the source of clostridium botulinum?

Answer 26

• canned or vacuum-packed foods

- ingestion of preformed toxin (inactivated by cooking)

Question 27

how does clostridium botulinum cause botulisism? tx?

Answer 27

• blocks ACh release from peripheral nerve synapses = paralysis
• treatment with antitoxin

Question 28

what does clostridium pefringens cause? source?

Answer 28

food poisoning (watery diarrhoea, cramps, vomiting lasting 24 hours)
source: reheated food (meat)
incubation = 8-16 hours

Question 29

what are the 2 toxins clostridium difficile produces?

Answer 29

pseudomembranous colitis

• Toxin A: enterotoxin = inflammation
• Toxin B = cytotoxin = virulence factor (more dangerous than A)

Question 30

which antibiotics are responsible for antibiotic related colitis?

Answer 30

• cephalosporins
• cipro
• clindamycin
  Tx: PO vancomycin

Question 31

describe listeria monocytogenes

Answer 31

• beta haemolytic
• aesculin positive
• tumbling-weed motility

Question 32

source of listeria monocytogenes

Answer 32

refrigerated food
unpasteurized dairy
vegetabloes
(grows at 4 degrees)

Question 33

what are the symptoms of listeria monocytogenes

Answer 33

watery diarrhoea
cramps
headache
fever
little vomiting

Question 34

who are at risk for listeria monocytogenes

Answer 34

perinatal infection
immunocompromised patients
elderly
BAD for pregnant women

Question 35

tx for listeria monocytogenes

Answer 35

ampicillin
ceftriaxone
cotrimoxazole