Food-borne infections and toxins Flashcards
What is the #1 cause of food-borne disease?
typhoid (vaccine not very effective still although more effective than it used to be)(Salmonella enterica)
What is the #1 water-borne disease?
cholera (Vibrio cholerae)
How are persistent food-borne diseases largely transmitted?
from animals via food
What is best way of not getting food-borne enteritis?
- cook food properly
- some foods develop toxins on standing after cooking
- cooked food can become contaminated from raw food or faeces
What are the 5 primary agents causing food-borne disease?
- Campylobacter
- Salmonella
- Listeria
- E.coli
- Norovirus
Name less important causes of food-borne illness and their most likely sources.
- S. aureus (nasal secretion)
- Bacillus cereus (rice)
- Clostridium perfringens type A (faeces)
- Clostridium botulinum (soil and faeces)
- Vibrio parahaemolyticus (shellfish)
- TSE (bovine neural tissues)
Why are steak burgers more likely to transmit food-borne disease than pieces of steak?
- 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’
What are the proportions of the main 5 pathogens in food (burden in terms of cases)
- campylobacter (60%)
- Norovirus (37%)
- Salmonella (3%)
- Listeria and E.coli 0157 (STEC) negligible amounts
What causes teh most hospital admissions?
> 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.
What causes most deaths with food-borne illness?
- campylobacter 30%
- salmonella (20% - i.e. lots of people who get salmonella die)
- E. coli and listeria (relatively high % cases die)
What was total 2011 cost of foodborne disease in england and wales
1564 million
Trend - campylobacter
- decreased in early 2000s, has been increasing since about 2005
Outline campylobacter jejuni (poultry) and C. coli (pigs)
- 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
Diagnosis - campylobacter
- 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
Outline campylobactr disease
- 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
How Campylobacter infection is acquired?
- 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
What are the different Campylobacter species?
- Campylobacter jejuni (poultry meat)
- Campylobacter coli (pigs, pork meat)
- Campylobacter upsaliensis (dogs)
T/F: cooking always kills Campylobacter
True
T/F: water baths for poultry are trying to be removed
True -
T/F: ice within inside of incompletely defrosted poultry still contains Campylobacter. Then cooking allows organism to grow –> campylobacter disease
True
What temperature can listeria grow
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)
Source of human listeriosis
- contaminated raw meat
- unpasteurised milk
- cheese made using unpasteurised milk
- foods containing raw veegetables (especially organic vegetables grown in well-manured soils)
Number of cases of human listeriosis in UK
200-250/year but can be nasty
Outline listeria transmission routes
Insert diagram
Outline listeria virulence
cell invasion, phagosomal escape, cytosolic replication and direct cell-cell sprea
Outline legislation gverning Listeria
- 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)
Who tends to be affected by listeria?
- immunocompromised individuals
- young
- elderly
- pregnant
- normal adults are relatively resistant to listeria
Is soft cheese dangerous in pregnancy?
often made with pasteurised milk so harmless - makes far more sense for pregnant women to not eat unpasteurised cheese
T/F: cooking always kills listeria monocytogenes
True
cases confirmed norovirus in UK
12,000-15,000 (these are reported, most likely 100,000)
What is norovirus?
= 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
T/F: cooking and disinfection always kills the virus
True
Dx - norovirus
- rt-qPCR assay most widely used
- unable to discriminate b/w infectious and non-infectious virus (by PCR/ any other method)
- culturing almost impossible
Another name E.coli 0157
STEC= shiga-toxin producing E. coli
- aka EHEC (enterohaemorrhagic E. coli)
- aka VTEC (verotoxigenic E. coli)
- often serotypes 0157:H7
What is the toxin of ETEC encoded by?
shiga-like toxin encoded by bacteriophage which infects the E.coli strain (toxins are ST-1 and ST-2)
Outline STEC in calves
- some diarrhoea and haemorrhagic colitis in calves
- causes effaced microvilli with E.coli pedestals (characteristic appearance)
Describe PH significance of STEC
- 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
Describe STEC human disease
- attaching and effacing lesions in gut (intimi)
- shiga-like toxin abosrbed –> vascular damage, oedema, thrombi
- thrombotic thrombocytopaenic purpurea
Dx - STEC
by culture of faeces (enrichment –> selective culture –> biochemical profile –> serotyping O and H antigens) and latex agglutination test
T/F: cooking destroys STEC
True (incidence/ prevalence has been decreasing in recent years)
What are the 2 different types of Salmonella?
- Salmonella enterica Typhimurium
- Salmonella enteria Enteritidis
T/F: many animals carry small numbers of Salmonella
True
Origin of human salmonellosis
- almost always originates with animal faeces: food, chicken on farms, adults on farms
T/F: cooking always kills Salmonella
True
Outline S. aureus as cause of food-borne illness
- 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!)
Outline Bacillus cereus and rice
- cooking rice activates spores
- toxin produced on rice during subsequent incubation
- eaten as reheated or fried rice
- keep rice cold before reheating next day???
Describe Clostridium perfringens type A
- from faeces
- 5% of strains produce CPE (enterotoxin)
- contaminated foodstuffs, incubated anaerobically, released on sporulation
Describe Clostridium botulinum
- faeces and soil
- botulinum toxin in heated, anaerobic foods, canned/bottled
- v rare in humans (a bit more common in USA)
What bacteria may be found in shellfish?
Vibrio parahaemolyticus
Why should raw meat be kept separate from cooked meat?
risk of cross-contamination (faeces)
Can you eat steak that has been in fridge for 3 weeks?
yes! surface contamination will be sorted by cooking when you sear the outside.
