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PMVPH (round 2) > Food-borne infections and toxins > Flashcards

Food-borne infections and toxins Flashcards

1
Q

What is the #1 cause of food-borne disease?

A

typhoid (vaccine not very effective still although more effective than it used to be)(Salmonella enterica)

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2
Q

What is the #1 water-borne disease?

A

cholera (Vibrio cholerae)

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3
Q

How are persistent food-borne diseases largely transmitted?

A

from animals via food

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4
Q

What is best way of not getting food-borne enteritis?

A
  • cook food properly
  • some foods develop toxins on standing after cooking
  • cooked food can become contaminated from raw food or faeces
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5
Q

What are the 5 primary agents causing food-borne disease?

A
  • Campylobacter
  • Salmonella
  • Listeria
  • E.coli
  • Norovirus
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6
Q

Name less important causes of food-borne illness and their most likely sources.

A
  • S. aureus (nasal secretion)
  • Bacillus cereus (rice)
  • Clostridium perfringens type A (faeces)
  • Clostridium botulinum (soil and faeces)
  • Vibrio parahaemolyticus (shellfish)
  • TSE (bovine neural tissues)
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7
Q

Why are steak burgers more likely to transmit food-borne disease than pieces of steak?

A
  • steak can get contaminated on outside of meat, inside muscle tissue can contain spores of bacteria (not harmful to humans - blackleg) but
  • minced meat is mixture of ‘inside and outside meat’
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8
Q

What are the proportions of the main 5 pathogens in food (burden in terms of cases)

A
  • campylobacter (60%)
  • Norovirus (37%)
  • Salmonella (3%)
  • Listeria and E.coli 0157 (STEC) negligible amounts
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9
Q

What causes teh most hospital admissions?

A

> 90% hospital admissions are caused by campylobacter.

  • almost all cases of E.coli and listeria end up in hospital
  • norovirus causes hospitalisation if concurrent disease.
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10
Q

What causes most deaths with food-borne illness?

A
  • campylobacter 30%
  • salmonella (20% - i.e. lots of people who get salmonella die)
  • E. coli and listeria (relatively high % cases die)
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11
Q

What was total 2011 cost of foodborne disease in england and wales

A

1564 million

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12
Q

Trend - campylobacter

A
  • decreased in early 2000s, has been increasing since about 2005
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13
Q

Outline campylobacter jejuni (poultry) and C. coli (pigs)

A
  • curved gram negative rod
  • very small
  • microaerophilic
  • can grow at 42 degrees (thus thermophilic)
  • endemic/enzooti in animls
  • carried by birds (especially poultry) and many mammals
  • zoonotic
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14
Q

Diagnosis - campylobacter

A
  • culture of faecal sample (gold standard) other methods do exist
  • blood agar with AB selection
  • 48 hours
  • 42 degrees microaerophilic atmosphere
  • demonstrate curved gram negative rods
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15
Q

Outline campylobactr disease

A
  • incubation 2-5 days
  • colonises the SI and enteritis
  • CS: diarrhoea, vomiting, stomach pains/cramps, fever (d/t invasion and signalling to innate immune system), unwell
  • commonest food poisoning in UK
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16
Q

How Campylobacter infection is acquired?

A
  • most raw poultry
  • raw meat
  • infected pets and farm animals
  • chickens are regularly colonised
  • factors processing of broilers
  • contamination of (inside of) carcass
  • freezing allows survival inside carcass
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17
Q

What are the different Campylobacter species?

A
  • Campylobacter jejuni (poultry meat)
  • Campylobacter coli (pigs, pork meat)
  • Campylobacter upsaliensis (dogs)
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18
Q

T/F: cooking always kills Campylobacter

A

True

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19
Q

T/F: water baths for poultry are trying to be removed

A

True -

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20
Q

T/F: ice within inside of incompletely defrosted poultry still contains Campylobacter. Then cooking allows organism to grow –> campylobacter disease

A

True

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21
Q

What temperature can listeria grow

A

8-10 degrees (fridges normally fluctuate between 4-10 degrees –> listeria can grow slowly)> leaving milk out on side allows listeria to grow! except pasteurisation prevents listeria being in milk in the first place)

22
Q

Source of human listeriosis

A
  • contaminated raw meat
  • unpasteurised milk
  • cheese made using unpasteurised milk
  • foods containing raw veegetables (especially organic vegetables grown in well-manured soils)
23
Q

Number of cases of human listeriosis in UK

A

200-250/year but can be nasty

24
Q

Outline listeria transmission routes

A

Insert diagram

25
Q

Outline listeria virulence

A

cell invasion, phagosomal escape, cytosolic replication and direct cell-cell sprea

26
Q

Outline legislation gverning Listeria

A
  • many strict rules
  • even lightly contaminated foodstuffs which is held in the fridge (especially when inefficient, perhaps 8-10 degrees, will allow listeria to grow such that it can have become heavily contaminated with listeria)
27
Q

Who tends to be affected by listeria?

A
  • immunocompromised individuals
  • young
  • elderly
  • pregnant
  • normal adults are relatively resistant to listeria
28
Q

Is soft cheese dangerous in pregnancy?

A

often made with pasteurised milk so harmless - makes far more sense for pregnant women to not eat unpasteurised cheese

29
Q

T/F: cooking always kills listeria monocytogenes

A

True

30
Q

cases confirmed norovirus in UK

A

12,000-15,000 (these are reported, most likely 100,000)

31
Q

What is norovirus?

A

= winter vomiting bug

  • ssRNA
  • person-person spread or foods and food handlers, faeces
  • calicivirus
  • small infective dose ( a single virus particle might be enough)
  • resistant in environment
32
Q

T/F: cooking and disinfection always kills the virus

A

True

33
Q

Dx - norovirus

A
  • rt-qPCR assay most widely used
  • unable to discriminate b/w infectious and non-infectious virus (by PCR/ any other method)
  • culturing almost impossible
34
Q

Another name E.coli 0157

A

STEC= shiga-toxin producing E. coli

  • aka EHEC (enterohaemorrhagic E. coli)
  • aka VTEC (verotoxigenic E. coli)
  • often serotypes 0157:H7
35
Q

What is the toxin of ETEC encoded by?

A

shiga-like toxin encoded by bacteriophage which infects the E.coli strain (toxins are ST-1 and ST-2)

36
Q

Outline STEC in calves

A
  • some diarrhoea and haemorrhagic colitis in calves

- causes effaced microvilli with E.coli pedestals (characteristic appearance)

37
Q

Describe PH significance of STEC

A
  • carriage by calves –> beef animals –> contaminated –> cooked foods
  • v low dose (10 CFU) infects humans (vs. 10 million salmonella needed for human infection)
  • causes haemorrhagic colitis and haemolytic uraemic syndrome leading to renal failure
38
Q

Describe STEC human disease

A
  • attaching and effacing lesions in gut (intimi)
  • shiga-like toxin abosrbed –> vascular damage, oedema, thrombi
  • thrombotic thrombocytopaenic purpurea
39
Q

Dx - STEC

A

by culture of faeces (enrichment –> selective culture –> biochemical profile –> serotyping O and H antigens) and latex agglutination test

40
Q

T/F: cooking destroys STEC

A

True (incidence/ prevalence has been decreasing in recent years)

41
Q

What are the 2 different types of Salmonella?

A
  • Salmonella enterica Typhimurium

- Salmonella enteria Enteritidis

42
Q

T/F: many animals carry small numbers of Salmonella

A

True

43
Q

Origin of human salmonellosis

A
  • almost always originates with animal faeces: food, chicken on farms, adults on farms
44
Q

T/F: cooking always kills Salmonella

A

True

45
Q

Outline S. aureus as cause of food-borne illness

A
  • in nasal secretions
  • 30% strains have ability to produce a heat-stable enterotoxin (thus even if foo dis boiled can cause illness)
  • vomiting 12 hours later for 12 hours then 12 hours later happy again (quick!)
46
Q

Outline Bacillus cereus and rice

A
  • cooking rice activates spores
  • toxin produced on rice during subsequent incubation
  • eaten as reheated or fried rice
  • keep rice cold before reheating next day???
47
Q

Describe Clostridium perfringens type A

A
  • from faeces
  • 5% of strains produce CPE (enterotoxin)
  • contaminated foodstuffs, incubated anaerobically, released on sporulation
48
Q

Describe Clostridium botulinum

A
  • faeces and soil
  • botulinum toxin in heated, anaerobic foods, canned/bottled
  • v rare in humans (a bit more common in USA)
49
Q

What bacteria may be found in shellfish?

A

Vibrio parahaemolyticus

50
Q

Why should raw meat be kept separate from cooked meat?

A

risk of cross-contamination (faeces)

51
Q

Can you eat steak that has been in fridge for 3 weeks?

A

yes! surface contamination will be sorted by cooking when you sear the outside.

PMVPH (round 2) (45 decks)

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