Food-borne Infections and Toxins

Question 1

What is food poisoning?

Answer 1

Food-borne infections in humans due to bacterial toxins in food leading to diarrhoea and vomiting which is occasionally severe or fatal

Question 2

What is the best way to make sure you don’t get food poisoning?

Answer 2

Cook your food properly

Question 3

What are the five main agents of concern?

Answer 3

Campylobacter - 60% of cases
Salmonella - 5 % of cases
Listeria - highest number of deaths
E. coli
Norovirus - 35% of cases

Question 4

What are some other kinds of food borne illness?

Answer 4

Staph aureus (nasal secretions)
Bacillus cereus (rice)
Clostridium perfringens Type A (faeces)
Clostridium botulinum (soil and faeces)
Vibrio parahaemolyticus (shellfish)

Question 5

What are the characteristics of Campylobacter species?

Answer 5

Curved gram negative rod
Microaerophilic at 42C
Endemic in animals, carried by birds and many mammals

Question 6

Which species of Campylobacter cause food poisoning?

Answer 6

C. jejuni from poultry

C. coli from pigs

Question 7

What is the pathogenesis of Campylobacter food poisoning?

Answer 7

Incubation period of 2-5 days
Colonises small intestine and causes enteritis
Diarrhoea, stomach pains, cramps, fever
Eat contaminated food to become infected

Question 8

How is Campylobacter diagnosed?

Answer 8

Faecal culture on blood agar with antibiotic selection for 48 hours at 42C in microaerophilic atmosphere

Question 9

How can Campylobacter food poisoning be prevented?

Answer 9

Cook food

Question 10

What makes Listeria different from other food poisoning bacteria?

Answer 10

Can grow at t stop it

Question 11

What is the source of infection for humans with Listeriosis?

Answer 11

Contaminated raw meat
Unpasteurised milk
Cheese made using unpasteurised milk
Foods containing raw vegetables

Question 12

Why is Listeria so virulent?

Answer 12

Invades the cell, escapes from the phagosome, replicates in the cytosol and spreads between cells directly

Question 13

Which groups of people are most at risk from Listeria?

Answer 13

Immunocompromised individuals
The young
The elderly
Pregnant women

Question 14

How can Listeriosis be prevented?

Answer 14

Cooking

Proper refrigeration

Question 15

What are the characteristics of Norovirus?

Answer 15

Calicivirus
Small infective dose
Resistant in the environment
Spread person to person or in foods or faeces

Question 16

What are the characteristics of E. coli O157?

Answer 16

Aka STEC

Shiga like toxin produced (ST-1 and ST-2)

Question 17

What is the public health significance of STEC?

Answer 17

Carriage by calves -> beef animals -> contaminated meat -> cooked foods
Very low dose (10 CFU) needed to cause infection in humans

Question 18

What are the clinical signs of STEC infection?

Answer 18

Haemorrhagic colitis and Haemolyti Uraemic syndrome causing renal failure

Question 19

What is the pathogenesis of STEC?

Answer 19

Attaches and effacing lesions in the gut caused by Intimin
Shiga like toxin is absorbed causing vascular damage, oedema and thrombi leading to thrombotic thrombocytopaenis purpurea

Question 20

How is STEC diagnosed?

Answer 20

Culture and Latex agglutination test

Question 21

What are the characteristics of Salmonella?

Answer 21

Many animals carry small numbers, infectious dose high
Vaccination programmes in poultry
Human salmonellosis originates from animal faeces on food/farms

Question 22

How is salmonellosis diagnosed?

Answer 22

Culture of faeces on enriched agar -> selective culture -> bochemical profile -> serotyping O and H antigens

Question 23

How does Staph aureus cause food poisoning?

Answer 23

From nasal secretions of food handlers

30% of strain produce an enterotoxin

Question 24

How does Bacillus cereus cause food poisoning?

Answer 24

Cooking rice activates spores, toxin produced on rice, eaten as reheated or fried rice

Question 25

How does C. perfringens cause food poisoning?

Answer 25

5% of strains produce enterotoxin (CPE)

Contaminated food stuffs, incubated anaerobically, released on sporulation

Question 26

How does C. botulinum cause food poisoning?

Answer 26

Botulinum toxin in heated anaerobic foods (canned/bottled)