Food Borne Pathogens

Question 1

What is the difference between an infection and intoxication?

Answer 1

Infection is caused by ingestion of a microorganism whereas intoxication is caused by ingestion of a toxin produced by a microorganism.

Question 2

Explain the difference between an invasive and toxico infection.

Answer 2

In an invasive infection the microorganism invades and penetrates intestinal mucosa (eg salmonella) whereas in toxico infection a bacteria produces toxin whilst in the intestinal tract (eg b. cereus)

Question 3

Outline the stages of the “meat chain”.

Answer 3

1. Pre-harvest - farm/market
2. Harvest - transport, lairage and abattoir
3. Processing and retail - supermarket, butcher, restaurant
4. Preparation and consumption - consumer

Question 4

What are the characteristic features of Yersinia enterocolitica?

Answer 4

• Gram -ve, non-sporogenic rods
• Facultative anaerobe
• Motility - motile at 22-25oC, non at 35-37oC
• Temp - 1-44 (optimum at 28-29oC)
• NaCl - 5-7%
• pH - 4-4.7

Question 5

Which biotypes of Yersinia are of greatest relevance in the EU?

Which livestock animal is of greatest concern here?

Answer 5

4 & 2

Pigs - throat, tonsils and faeces.

Question 6

What control methods should be taken throughout the meat chain to reduce the risk of Yersiniosis?

Answer 6

1. Pre-harvest - biosecurity on farm, stress management
2. Harvest - abbatoir - risk categories, remove head and tie rectum
3. Post-harvest - correct procedures for processing, storage and prep/consumption

Question 7

Desribe a case of Yersiniosis in a human.

Answer 7

• Incubation - 1-11days with <10^4 cells
• Acute - gastroenteritis, fever, pseudo-apendicitis and ~bloody diarrhoea
• Seconary complications (1-3 wks) - arthritis, erythma nodosum and myositis

Question 8

Name 4 products which can harbour Yersinia.

Answer 8

1. Pig - raw products (tongue, meat)
2. Cattle - carriers or cross-contamination from pig meat
3. Milk - poor pasteurisation
4. Vegetable - poor meat storage

Question 9

Name the three relevant species of Vibrio bacteria.

Answer 9

• cholerae
• parahaemolyticus
• vulnificus

Question 10

What are the morpho/physiological features of V. cholerae?

What is the main source of this bacteria?

Answer 10

• Facultative anaerobe
• Halophilic - NaCl 0.5-10% (seawater)
• Alkaliphilic - pH 7.8-8.6
• Straight/curved motile rods
• Temp - 10-19oC

Main source is faecally contaminated water. (also contaminated shellfish)

Question 11

Describe the pathogenesis and symptoms of cholera.

How can infection be controlled?

Answer 11

Incubation - 6h-5d.

Cholera is a toxico-infection caused by enterotoxic.

Symptoms include profuse, watery diarrhoea, severe abdominal pain and vomitting. Secondary - dehydration, acidosis, shock and circulatory collapse, death.

Control - avoid contaminated water, waste disposal, controll infectious individuals, chill foods correctly

Question 12

Which toxin is released by V. parahaemolyticus?

What is the incubation period for disease and what are the symptoms?

Answer 12

Haemolytic cytotoxin

Incubation is 12-24hrs, symptoms are similar to V. cholerae but more mild.

Question 13

Answer:

1. Incubation period of V. vulnificus.
2. Symptoms of infection
3. Infectious dose.

Answer 13

1. 16-38h
2. Severe - septicaemic invasive infection, fever, nausea, necrotic skin lesions, death
3. Low dose - up to 100 cells

Question 14

What is the main relevant species of Listeria?

What are the main sources of this species?

Answer 14

Listeria monocytogenes

• Animal and human intestines - assymptomatic carrier
• Ubiquitous in the environment - soil, water, plants, silage
• Work surfaces - persistant biofilms
• Ready-to-eat foods - raw milk, soft cheese, post production contamination of meat, veg, salad, unpasteurised juice

Question 15

What are the characteristic features of L. monocytogenes bacteria?

Answer 15

• Gram +ve rod
• Motility - motile @ 25oC, non-motile @ 37oC
• Facultative anaerobe - prefers microaerophilic if O2 present
• Resistance to drying
• Temp - 4 (or lower) - 45oC
• Tolerent up to 10% NaCl, low aw
• pH - 4.1 - 9.6

Question 16

Describe the pathogenesis of Invasive Listeriosis.

Which groups are particularly at risk if they contract the disease?

Answer 16

1. Incubation - 1-21 days. Invades GI mucosa then macrophages and travels via the blood stream to CNS or foetus
2. Pregnant women, AIDS, cancer, young and elderly
   
   1. Abortion, Septicaemia, Encephalitis

Question 17

Symptoms of non-invasive listeriosis.

Answer 17

Enteric diarrhoea, mild fever, headach and myalgia.

Incubates for 1-3 days

Question 18

What control measures should be employed for the control of Listeriosis?

Answer 18

1. HACCP
2. Avoid high risk foods if at risk category
3. No unpasteurised products
4. Prevent cross contamination of raw and processed products
5. Re-heat ready-to-eat foods adequately

Question 19

Name three gram positive toxigenic bacteria?

What is the toxic dose of each of the toxins which they produce? (cells/gram)

Answer 19

• S. aureus 10^6
• C. botulinum 10^4 - 10^5
• B. cereus 10^7 - 10^8

Question 20

What are the characteristic features of Staphylococcus aureus?

What toxins are produced by the bacteria?

Answer 20

• Non-motile, facultative anaerobe cocci
• Temp - 7-46°C (enterotoxin not produced <8°C)
• pH: 4-9.8
• Tolerate low aw - resistant to desiccation
• Tolerate 10% NaCl (and produce enterotoxin A)

8 toxins (A, B, C1, C2, C3, D, E, F) most common type A, then D

Question 21

What is the incubation period and main symptoms of S. aureus toxico-infection?

Answer 21

Incubation period 1 - 6h with main symptoms starting at 6 to 24h.

• nausea
• vomiting & diarrhoea
• abdominal pain
• NO fever
• collapse and dehydration

Question 22

What number of S. aureus colonies are required to produce enough toxin in food to produce illness?

Answer 22

>10^5 CFU/g

Question 23

Outline control measures which can be used to control S.aureus infection.

(x6)

Answer 23

1. Good personal hygiene practices
2. Don’t handle food with skin infections
3. Chill cooked food rapidly in small quantities
4. Store cooked or heat-treated foods at <4°C or >60°C.
5. Avoid extensive handling of foods.
6. Avoid delays between cooking and eating.

Question 24

C. botulinum toxin poisoning causes what symptoms?

Answer 24

Blocks nerve synapsis causing paralysis and death

Question 25

What are the main sources of C.botulinum toxin poisoning? Name the two types of toxin poisoning and describe their origin.

Answer 25

Sources: Soil , water, vegetables – Animal and human faeces (asymptomatic) 1. Botulism (intoxication) 2. Infant botulism (toxico-infection)

Question 26

Describe the onset, duration and symptoms of C. botulinum proteolytic and non-proteolytic toxicoinfection. How does the toxic dose of proteolytic and non-proteolytic toxin differ?

Answer 26

1. onset - 12-36 hours 2. duration - days to several months 3. symptoms - nausea vomiting visual disturbances, vertigo Toxic dose: * Proteolytic - 0.005-0.1mcg * Non-proteolytic - 0.1-0.5mcg

Question 27

Outline the differences between proteolytic and non-proteolytic C.botulinum bacteria.

Answer 27

Bold values are proteolytic: * toxin types **A, B, F** B, E, F * minimum pH **4.6** 5 * maximum NaCl **10 %** 3 % * minimum aw **0.93** 0.97 * temp. range for growth **12.5 - 48°C** 3.5 - 48°C * decimal reduction time of spores at 100°C **25 min.** \<0.1 min.

Question 28

Which food product poses high risk to infants through its potential to cause infant botulism? Why are they at risk?

Answer 28

Honey Children under 1 year old do not have established gut microflora, so the pathogen may colonize more easily than in other individuals.

Question 29

What control measures should be undertaken to reduce the risk of C. botulinum poisoning?

Answer 29

1. Avoid home canning of vegetables, fish and meats. 2. Discard cans with faulty seals. 3. Heat any suspect food to 80°C for 15 minutes to destroy toxin. 4. Store home-canned foods at \<3°C. 5. Do not feed honey to babies or infants. 6. Do not feed infants non-heat treated foods

Question 30

This spore-forming, gram positive rod is associated with pulses and rice food poisoning. Name the bacteria and describe the two toxins which it produces.

Answer 30

Bacillus cereus 1. Emetic toxin induces rapid and profuse vomitting in 15 minutes 2. Enteric toxin induces profuse, painful but shortlived diarrhoea after 4-6 hours

Question 31

Bacillius cereus requires **x** of bacteria in incriminating food.

Answer 31

10^8 cells/g

Question 32

How long do symptoms of emetic and enteric B.cereus poisoning last?

Answer 32

Enteric - 12 - 24 hours Emetic - 6 - 36 hours

Question 33

What thermal values at which time length are capable of destroying B.cereus?

Answer 33

D-values: 0. 02 - 0.06 minutes at 121°C 0. 3 - 27 minutes at 100°C

Question 34

These cooked and raw foods are high risk in terms of B.cereus.

Answer 34

1. Raw foods 1. cereals 2. dried vegetables, potatoes 3. milk/ cream 4. rice 5. spices 2. Cooked / processed foods 1. roast / fried meat products 2. soups 3. cooked / fried rice meals

Question 35

Name the toxins of relevance produced by C.prefringens.

Answer 35

Type A toxin producing strains survive in **animal GI tract and soils** β-toxin producing type C strains may cause **acute necrotizing** GI disease

Question 36

Name the viruses which can cause food poisoning in humans. Briefly describe each.

Answer 36

1. Rotavirus - young children - perfuse and projectile vomiting (damages intestinal mucosa) 2. Calicivirus - young and adults - fevers, headache and abdominal pain as well as D & V 3. Hepatitis 1. A - person-to-person, anal intercourse, faecal contamination - shellfish - liver and GI invasion 2. E - pork and processed pork products (british-style)