Food Borne Infections And Toxins Flashcards
Give 2 old food borne diseases
- both spread feacal oral route*
> typhoid - enteric fever caused by salmonella enterica Typhi, survives in macrophages, causes sepsis
- still present throughout the world but eradicated from UK
- carriers (GIT cells or gall bladder) can infect others, eradication hard
> cholera - water borne
- vibrio cholerae
What is the best way to avoid food-borne enteritis ?
Cook your food properly
- but some foods eaten raw or rare
- can develop toxins on standing
- cooked food can be contaminated from raw food/feaces
5 primary agents of food borne disease in the UK
Campy Salmonella Listeria E. Coli Novovirus (Severity and no cases in hospitals)
Other causes food borne illness LOOK
- s alerts Bacillus cerise C perfringens Yule a Botulism ---
Why are burgers more likely to cause food poising than steak?
Ground meat contaminated throughout burger
- steaks only contaminated on the outside (inside equivalent to sterile wrt human pathogens)
Which pathogen accounts for majority of numbers of food poisoning
- campy 60%
- nori virus 30%
- salmonella very few
- norovirus and listeriosis very minimal
Which pathogens cause majority of HOSPITAL admission
- majority campy
- salmonella
- E. coli
- listeria
- norovirus (if immunocompromised/concurrent disease)
Which pathogens cause majority of deaths from food poisoning?
- campy 30%
- salmonella 20%
- E. coli 10%
- listeria 30%
- norovirus 10%
How has incidence of campy changed over time?
- was dropping
- since 2005 increasing again and now at higher level than initially
What is campy ? Subspecies? Diagnosis? How is it cultured? Incubation period?
- campylobacter jejuni (poultry)
- campylobacter coli (pigs)
- campylobacter upsaliensis (dogs)
> microaerophilic, 42*
> endemic in animals (birds and mammals) - dx by culture of feacal sample
- zoonotic*
-2-5d incubation period
Pathogenesis of campylobacter
- colonised SI
- VD+ stomach pains
- fever (so innate immune system activated)
Majority of infection with campylobacter from which sources?
- most raw poultry
- raw meat
- infected pets and farm animals
Dx of campy?
- culture feacal sample
- blood agar with Abx selection
- 48hrs 42* microaerophilic
- curved G- rod
How can campylobacter be controlled?
COOKING ALWAYS KILLS CAMPY!
How does meat handling allow for campy growth
- not properly defrosted chicken
- frozen centre allows survival inside carcasse
What makes listeria monocytogenes special?
Can grow in the fridge (8-10*)
Sources of infection of listeria
- contaminated raw meat
- unpasteurised milk (pasteurising destroys listeria well)
- cheese made with unpasteurised milk
- foods containing raw vegetables
- esp organic vegetables in well manured soils
Incidence of listeriosis over time?
Roughly stable around 150 cases/year
How is listeria transmission?
- soil
- silage (can grow here)
- ingestion by animals -> encephalitis, bacteria email and abortion
- meat
- feaces
- udder -> dairy products
- humans
How is listeria virulent?
- get inside enterocytes
- produce haemolysin
- produce polymerised actin to propel into adjacent cells
- hide in cytoplasm safe from Abx and immune
Is listeria monitored and controlled tightly?
YES
- legislation
Who is commonly affected by listeria?
- immunocompromised individuals
- Young old
- pregnant women (people say don’t have soft cheese - no reason for this! Don’t have unpasteurised cheese)
- normal adults relatively resistant to disease
How can listeria be destroyed
COOKING ALWAYS KILLS LISTERIA
how has incidence of norovirus changed?
- increasing
- no actual cases 150-200,000 cases/year (lab confirmed cases 10x less than this)
What is norovirus ? Method of spread?
- winter vomintiing bug
- ss RNA virus
- person to person spread, food and food handlers, fomites
- feaces
> calicivirus - single virus needed to infect, very resistant in the environment.
Dx of. Novirus
- RT qPCR
- unable to differentiate infective and non infective
- dx hard
How can norovirus be destroyed?
Proper disinfection and cooking
Incidence of E. Coli?
Stable but numbers higher than they should be!!
What is e. Coli
- Stec
- e. Coli 0157 (mostly, not all strains are this)
> bacteriophage transmits ability to product toxin (ST1 and ST2)
Does E. coli affect aniamlsb
Haemorrhagic D+ in calves but not major problem
- esp infects beef
Pathogenesis of E. coli STEC infection
- destruction of villi
- pedestals little spheres seen on micro villi characterstic
Is a high dose of E . Coli needed to cause disease? How does this compare tosalmonella?
- high dose salmonella needed
- low dose E. coli needed
Clinical, signs E. coli
- haemorrhagic colitis
- haemolytic ureamic syndrome -> renal failure
How have incidence of salmonella changed?
- decrease
- d/t testing and vaccination of poultry
Salmonella
S e term a typhimurium (poultry) S enteridis (eggs)
Infectious dose salmonella
High ( relatively, still not much)
- animal feaces (human to human transmission poss but rare)
How have salmonella incidence been decreased?
Vaccination laying flocks
How can salmonella be destroyed?
Cooking
Dx salmonella
Enrichment selective media
- biochem serotyping O and H ???
How does s. Aureus cause food poisoning?
- 40% strains can produce heat stable enterotoxin (NOT DESTROYED BY COOKING)
- nasal secretion
Incubation period of s aureus? How long does it cause disease for?
12 hours
- > 12 hours V+
- > then resolves spontaneously (only toxin ingested, no bacterial invasion etc.)
How does bacillus cereus cause food poisoning?
- Cooking rice activates spores from bacillus cereus
- toxin produced on rice during subsequent incubation (eaten as reheated or fried rice)
- need to keep rice cold between cooking and reheating
How does clostridium perfringens type a cause food poisoning?
- feaces
- 5% strains produce enterotoxin
- contamination food stuffs incubated anaerobically
- released on sporulation
How does clostridium botulinum cause disease?
- from feaces and soil
- heated then bottled/canned (anaerobic)
- botulinum toxin present
- more common USA than UK
- can kill cattle if food left too
What is vibrio parahaemolyticus associated with?
- shell fish
Can you eat a 3 week old steak if it has been kept in the fridge?
Yes micro biologically safe!!
What can cause food poisoning?
Food borne infections
Bacterial toxins in food
