GI Microbiology

Question 1

The factor of foreign travel implies what?

Answer 1

Traveller’s diarrhoea: entertoxigenic E. coli
South east Asia: vibrio species
South America, Asia, Africa: rotavirus

Question 2

A recent course of antibiotics implies what?

Answer 2

An increased risk of Clostridium difficile infection

Question 3

Daycare exposure implies what?

Answer 3

Rotavirus

Question 4

Exposure to raw seafood implies what?

Answer 4

Non-cholera vibrio

Question 5

Patients who have anal receptive sex (MSM) implies what?

Answer 5

Shigella
Campylobacter
Salmonella

Question 6

Patient’s with a HIV-positive status implies what?

Answer 6

Mycobacterium avium-intracellular complex
Cytomegalovirus
Giarda

Question 7

What do outbreaks imply?

Answer 7

Cruise ships - norovirus

Contaminated local source: campylobacter, E. coli

Question 8

Bacillus cereus

Answer 8

Gm + bacillus
In starchy foods like rice
Has heat resistant spores
Causes profuse vomiting
Short incubation 1-6 hours

Question 9

Staphylococcus aureus

Answer 9

Gm + coccus
Source: food left at room temp (milk, meat, fish)
It’s toxin is pre-formed in food causing rapid absorption
Acts on VC and also causes abdo pain

Question 10

Shigella

Answer 10

Endemic in the developing world

Shiga toxin will bind to receptors on renal cells, RBCs, and others inhibiting protein synthesis and causing cells death

Question 11

E. Coli 0157

Answer 11

Suspect: bloody diarrhoea/blood PR
Very low infectious dose
Source: wide range of food, person to person and animal contact
50% of cases < 16 years old
Highest rate < 5 years old

Question 12

Haemolytic Ureamic Syndrome

Answer 12

8-15%of E. coli 0157cases within 2 weeks
Symptoms and signs: abdo pain, fever, pallor, petechiae, Liguria, bloody diarrhoea, increased WBC, decreased platelets, red cell fragments, LDH > 1.5x normal

Question 13

What are the investigations for HUS?

Answer 13

Stool samples
U&Es
FBC
clotting
Urine
Lactate dehydrogenase

Question 14

What do you not do for HUS?

Answer 14

No antibiotics
No anti motility
No NSAIDS

Question 15

Campylobacter

Answer 15

Incubation: 16-48 hours
Source: food; raw poultry, raw milk
Symptoms and signs: pain, blood (30%), fever
Treatment: macrolides (if co-morbid factors but increasingly resistant)
Most common GI infection, it has small pathogen numbers and is invasive
Less likely to spread from person to person

Question 16

Salmonella enteritis

Answer 16

Incubation: 12-48 hours
Source: food; poultry, meat, raw eggs; animal gut, multiplies in food
Symptoms and signs: diarrhoea and vomiting, blood, fever

Question 17

Typing salmonella

Answer 17

Different antigens on the body, called O antigen
Antigen agglutinates with corresponding antibody

Serogrouping salmonellae can help pinpoint the source of infection
Groups B, C & D are most common locally/
Serogroups are further divided by looking at antigens on the tail

Question 18

Listeria monocytogenes (Gastroenteritis)

Answer 18

Incubation: 9-48 hours
Symptoms and signs: fever, muscle aches, diarrhoea, pregnant women may have mild symptoms
Source: unpasteurised milk products, deli counter
“Fridge bacteria”

Question 19

Listeria monocytogenes (Gastroenteritis)

Answer 19

2-6 weeks

Patients at risk: immunosuppressive (esp. T cell), age >50, pregnancy

Question 20

Diagnosis of Listeria

Answer 20

Easier from sterile site
Gm + rod
Cold enrichment
Culture

Question 21

Rotavirus

Answer 21

Commonest in kids < 3
Almost all kids get it before 5
Spread: person to person, faecal-oral
Usually in the winter
Can be severe in the immunocompromised
Symptoms: moderate fever, vomiting, diarrhoea, NOT bloody
Self-limiting, lasts a week
Low infectious dose, survives in the environment
Hydration is key management

Question 22

Norovirus

Answer 22

Affects all ages: highly infectious
Route: faecal-oral droplet, person to person, environmental survival on fomites
Low infectious dose
Diarrhoea and vomiting, explosive and sudden
Lasts 2-4 days, usually self limiting
Early ward closure/isolation/cohorting required