Bacterial foodborne pathogens

Question 1

Give a definition of foodborne intoxication

Answer 1

The organism produced specific toxins or toxic metabolites in the food that in ingested
e.g. C.botulinum, Staph.aureus, Bacillus cereus

Question 2

Define a foodborne invasive infection

Answer 2

Bacteria ingested through food consumption, the organism invades and penetrates the intestinal mucosa - don’t possess toxins
e.g. Salmonella, campylobacter, listeria

Question 3

Define a foodborne toxico-infection

Answer 3

Bacteria ingested through food consumption, the organism produces toxins whilst in the GI tract
e.g. E.coli, Vibrio cholerae, C.perfringens

Question 4

Describe the features of Yersinia enterocolitica

Answer 4

Gram -ve, small rod shaped
Wide temp range
Heat resistance about 60
4-4.7 pH range

Question 5

Describe the symptoms of a Yersinia infection

Answer 5

Gastro-enteritis with diarrhoea and/or vomiting; however, fever and abdominal pain are the hallmark symptoms
24-48 hrs incubation

Question 6

What are the main food sources of Yersinia

Answer 6

Pork (main reservoir), dairy products, fish, other meats

Question 7

What are some pre-harvest control measures for Yersinia enterocolitica?

Answer 7

Prevention of introduction on the farm
Prevention of spread
Hygienic husbandry 
Removal of seropositives from the herd
Clean water, prevent faecal contamination of water and feed

Question 8

What are some post-harvest control measures for Yersinia enterocolitica?

Answer 8

Maintaining the cold chain
Raw pork separate from other foods
Proper cooking regime
Personal hygiene
Cleaning and disinfection

Question 9

What are some features of Vibrio cholerae?

Answer 9

Gram negative rods
Anaerobic
Non-spore forming 
Halophilic (low NaCl conc)
Alkaliphilic 
Growth in water 
Heat sensitive
Sensitive to drying and freezing below -20

Question 10

What are the main symptoms of Vibrio cholerae infection?

Answer 10

Profuse, watery diarrhoea with vomiting and muscle cramps lasting for a few days; dehydration and salt imbalance may follow
Onset is usually rapid and patients may dehydrate
within hours if not treated

Question 11

What are the main sources of Vibrio cholerae?

Answer 11

Faecal contaminated water
Person to person spread
Poor sanitation
Raw fish and shellfish harvested from polluted waters

Question 12

How is vibrio cholerae treated?

Answer 12

With proper oral and/or intravenous rehydration therapy, treatment is simple and effective; case fatality rates are <1%.
Antibiotics are not usually needed

Question 13

Which 3 bacteria cause toxication due to a toxin produced in the food?

Answer 13

• Bacillus cereus
• Clostridium botulinum
• Staphylococcus aureus

Question 14

Name the bacteria causing this infection:

• No fever, but vomiting, diarrhoea, abdominal pain
• Enterotoxin is highly heat resistant
• Main sources: skin, milk, environment

Answer 14

Staphylococcus aureus

Question 15

What are the 2 types of clostridium botulinum infections?

Answer 15

Botulism - intoxication

Infant botulism - toxico-infection

Question 16

What is the most common source of infant botulism?

Answer 16

Honey

Question 17

What are the two syndromes caused by bacillus cereus?

Answer 17

Emetic = intoxication 
Diarrhoeal = toxico-infection

Question 18

Which bacteria is most likely to grow on rice that has not been chilled or reheated appropriately?

Answer 18

Bacillus cereus - emetic syndrome