bacterial gastointestinal infections

Question 1

food-borne gasto disease

Answer 1

• Preformed toxin
Staphylococcus aureus, Bacillus cereus,

• Toxin production in gut
Clostridium perfringens, Bacillus cereus,
Enterotoxigenic E.coli, Vibrio cholera

• Tissue invasion
Campylobacter, Salmonella, E.coli O157
(Not Listeria, botulism)

Question 2

pathogensis

Answer 2

• Ingestion, survival, adhesion to mucosa
• Normal flora; colonisation resistance
(anaerobes, E.coli, coliforms……)
• Infective dose
• Toxin production (cholera)
• Toxin production/mucosal invasion
(salmonella, shigella)
• Diarrhoea; mechanism of spread

Question 3

lab diagnosis

Answer 3

• Microscopy; parasites only
• Culture on selective indicator media

• Identification
Biochemical tests
Morphology
Agglutination with
specific antisera

• Toxin detection

Question 4

ecoli

Answer 4

• Important part of gut normal flora
• Important pathogen; UTI, abscesses,
septicaemia
• Gastrointestinal disease
enterotoxigenic
enteroaggregative
enteroinvasive (shigella)
enterohaemorrhagic (0157)

Question 5

travellers diarrhoea

Answer 5

• Epidemiology:
World-wide
Developed-developing countries
• Clinical:
Diarrhoea +/- nausea, vomiting, pain
• Pathogenesis:
Enterotoxigenic E.coli (40%)
Entertoxin mediated (cholera-like toxin)
• Treatment:
Symptomatic
Ciprofloxacin shortens period of symptoms, but sideeffects/ resistance (controversy)

Question 6

verocytotoxin-prodcing e.coli

Answer 6

• Epidemiology:
Zoonosis
Food-borne/person-person
Low infecting dose (<10orgs)
Under-cooked meat, summer peak

• Pathogenesis:
Serotype 0157, few others
Toxin production-mucosal invasion

• Clinical:
Bloody diarrhoea, pain, fever
Haemorrhagic colitis
Haemolytic Uraemic Syndrome

• Management:
Symptomatic, supportive
?role of antibiotics

Question 7

HUS

Answer 7

• Thrombocytopaenia, microangiopathic
haemolytic anaemia, renal failure
• 90% associated with VTEC, mainly O157
• 70% recovery
• 5% mortality

Question 8

shigella

Answer 8

• Epidemiology:
Human reservoir
Low infecting dose (10orgs)
Faecal-oral spread; occasionally food-borne
Children; household, schools
Inc. period 1-7days

• Pathogenesis:
Shigella dysenteriae; S.flexneri, S.boydii, S.sonnei (UK)
Toxin production-mucosal invasion

• Clinical:
Mild diarrhoea; most cases of sonnei
Severe dysentery; fever, bloody diarrhoea, pain
Toxic megacolon

• Management:
Symptomatic
Antibiotics for severe disease only

Question 9

campylobacter

Answer 9

• Epidemiology:
Zoonosis; multiple animal reservoirs
Most common bacterial cause of food poisoning
Under-cooked meat

• Pathogenesis:
Campylobacter jejuni mainly; occasionally C.coli (spiral)
Mucosal invasion

• Clinical:
Inc. period 3-5days
Mild to severe diarrhoea, sometimes bloody, pain, fever
Rarely septicaemia
Rare complications include reactive arthritis, Guillan-Barre
syndrome

• Management:
Symptomatic
Clarithromycin for severe cases

Question 10

salmonella

Answer 10

• Epidemiology:
Zoonosis
Under-cooked meat; cross-contamination; eggs
Direct spread unusual; replication in food necessary to
reach infecting dose

• Pathogenesis:
Salmonella enteritidis; multiple strains (names)
Toxins/ direct mucosal invasion

• Clinical:
Inc period 12-72 h; diarrhoea , pain, fever, vomiting
Septicaemia in elderly, infants, immunocompromised

• Management:
Symptomatic
Antibiotics for septicaemia

Question 11

enteric fevers

Answer 11

• Typhoid/paratyphoid
• Salmonella typhi; Salmonella paratyphi A,B,C
• Human reservoir
• Invasive, multi-system disease
• PUO
• Gastrointestinal symptoms minimal

Question 12

cholera

Answer 12

• Epidemiology:
Human reservoir
Waterborne/ food occasionally
Poor sanitation; war/natural disasters
Pandemics; new strains (classical; El Tor)
• Pathogenesis:
Vibrio cholera (curved)
Toxin-mediated

• Clinical:
Inc period 1-5 days; painless severe diarrhoea
and vomiting;
Rice-water stools: dehydration risk
• Management:
Fluids/electrolytes
Tetracycline reduces diarrhoea/ excretion
• Prevention:
Killed whole cell oral vaccine; 50% protection, short-term

Question 13

cholera mechanisms of action

Answer 13

Question 14

c.diff

Answer 14

Epidemiology:
Human reservoir; ~5% faecal carriage
Hospital cross infection
Pathogenesis:
Overgrowth of organism associated
with reduced normal gut flora during
antibiotic treatment (broadspectrum)
Toxin A and B production

• Clinical:
Mild to severe watery diarrhoea
Pseudomembranous colitis
• Laboratory diagnosis:
Toxin detection
Culture for epidemiological typing
• Management/ prevention:
Supportive
Metronidazole or oral vancomycin
Infection control procedures
Appropriate use of antibiotics

Question 15

staph

Answer 15

• Epidemiology:
Contamination of ready to eat food
from hands of food handler,
followed by temperature abuse
• Pathogenesis:
Toxin-producing Staphylococcus aureus
Toxin production in food; ingest toxin
Neurotoxin; vomiting centre
• Clinical:
Incubation period 1-6hrs
Abrupt onset of nausea, vomiting, cramps
• Diagnosis:
Enterotoxin detection in faeces and food

Question 16

clost

Answer 16

• Epidemiology:
Bulk cooked meat dishes; anaerobic conditions
• Pathogenesis:
Spores survive cooking
Germination/growth during slow cooling or warming
Organisms ingested, sporulate in gut releasing toxin
• Clinical:
Incubation period 12-24 hours
Diarrhoea, cramps
• Diagnosis:
Culture food

Question 17

cabillus cereus

Answer 17

• Epidemiology:
Boiled/fried rice reheated in bulk
• Pathogenesis:
Spore-forming organism
Toxin production in food or following ingestion of
organism
• Clinical:
Emetic form; inc period 1-6 hours
Diarrhoeal form; inc period 8-16 hours