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PHEW > Food Borne Pathogens > Flashcards

Food Borne Pathogens Flashcards

1
Q

What is the difference between an infection and intoxication?

A

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

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2
Q

Explain the difference between an invasive and toxico infection.

A

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)

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3
Q

Outline the stages of the “meat chain”.

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

What are the characteristic features of Yersinia enterocolitica?

A
  • 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
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5
Q

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

Which livestock animal is of greatest concern here?

A

4 & 2

Pigs - throat, tonsils and faeces.

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6
Q

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

A
  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
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7
Q

Desribe a case of Yersiniosis in a human.

A
  • 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
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8
Q

Name 4 products which can harbour Yersinia.

A
  1. Pig - raw products (tongue, meat)
  2. Cattle - carriers or cross-contamination from pig meat
  3. Milk - poor pasteurisation
  4. Vegetable - poor meat storage
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9
Q

Name the three relevant species of Vibrio bacteria.

A
  • cholerae
  • parahaemolyticus
  • vulnificus
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10
Q

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

What is the main source of this bacteria?

A
  • 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)

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11
Q

Describe the pathogenesis and symptoms of cholera.

How can infection be controlled?

A

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

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12
Q

Which toxin is released by V. parahaemolyticus?

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

A

Haemolytic cytotoxin

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

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13
Q

Answer:

  1. Incubation period of V. vulnificus.
  2. Symptoms of infection
  3. Infectious dose.
A
  1. 16-38h
  2. Severe - septicaemic invasive infection, fever, nausea, necrotic skin lesions, death
  3. Low dose - up to 100 cells
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14
Q

What is the main relevant species of Listeria?

What are the main sources of this species?

A

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
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15
Q

What are the characteristic features of L. monocytogenes bacteria?

A
  • 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
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16
Q

Describe the pathogenesis of Invasive Listeriosis.

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

A
  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
17
Q

Symptoms of non-invasive listeriosis.

A

Enteric diarrhoea, mild fever, headach and myalgia.

Incubates for 1-3 days

18
Q

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

A
  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
19
Q

Name three gram positive toxigenic bacteria?

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

A
  • S. aureus 10^6
  • C. botulinum 10^4 - 10^5
  • B. cereus 10^7 - 10^8
20
Q

What are the characteristic features of Staphylococcus aureus?

What toxins are produced by the bacteria?

A
  • 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

21
Q

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

A

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

  • nausea
  • vomiting & diarrhoea
  • abdominal pain
  • NO fever
  • collapse and dehydration
22
Q

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

A

>10^5 CFU/g

23
Q

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

(x6)

A
  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.
24
Q

C. botulinum toxin poisoning causes what symptoms?

A

Blocks nerve synapsis causing paralysis and death

25
Q

What are the main sources of C.botulinum toxin poisoning?

Name the two types of toxin poisoning and describe their origin.

A

Sources: Soil , water, vegetables – Animal and human faeces (asymptomatic)

  1. Botulism (intoxication)
  2. Infant botulism (toxico-infection)
26
Q

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?

A
  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
27
Q

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

A

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.
28
Q

Which food product poses high risk to infants through its potential to cause infant botulism?

Why are they at risk?

A

Honey

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

29
Q

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

A
  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
30
Q

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.

A

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
31
Q

Bacillius cereus requires x of bacteria in incriminating food.

A

10^8 cells/g

32
Q

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

A

Enteric - 12 - 24 hours

Emetic - 6 - 36 hours

33
Q

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

A

D-values:

  1. 02 - 0.06 minutes at 121°C
  2. 3 - 27 minutes at 100°C
34
Q

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

A
  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
35
Q

Name the toxins of relevance produced by C.prefringens.

A

Type A toxin producing strains survive in animal GI tract and soils

β-toxin producing type C strains may cause acute necrotizing GI disease

36
Q

Name the viruses which can cause food poisoning in humans.

Briefly describe each.

A
  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)

PHEW (6 decks)

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