Food poisoning

What is the vets role in human health relating to food poisoning?

Food poisoning is a zoonotic disease

Vets role is to prevent these diseases in animals

How does salmonella cause human food poisoning?

A pathogen of animals

The animal may or may not recover making it into a carrier of the disease

How do EHEC and Camploybacter cause human food poisoning?

EHEC carried by cattle but does not effect them

Campylobacter carried by chickens

They are commensals (normal flora, part of the animals microbiota)

How does Clostridium botulinum cause human food poisoning?

Microorganims may be introduced into or on the surface of food

What are the usual symptoms of food poisoning?

Fever, abdominal pain, diarrhoea and vomiting

What is infection-type food poisoning?

Ingested, may sit on tissue or invade tissues producing inflammation

Salmonella, Campylobacter, E. coli

What is toxin-type food poisoning?

Toxin gives symptoms by ingestion - symptoms only caused by toxin

Staphylococcus aureus - enterotoxin

Clostridium botulinum - neurotoxin

Describe the structure of campylobacter

Slender, motile, Gram negative curved or spiral rods

Campylobacter is microaerophilic, what does this mean?

It needs reduced O2 for growth

5% O2, 10% CO2, 85% N2

What does campylobacter cause?

Most frequently identified cause of acute infective bacterial diarrhoea in humans - acquire from food

How can cross contamination of campylobacter be caused?

If not kept away from other foods that won't be cooked at high temperatures

What is occupational zoonosis?

People who are exposed to animals through work are more likely to be infected

What is a serotype?

An antigenic variant in surface antigens within a species

What is the difference between a strain and a serotype?

A strain is a specific type of one disease (species)

A serotype is a is an antigenic variant in surface antigens of a species

e.g. there are different serotypes within the strain, Salmonella enterica

What are the two important strains of salmonella?

S. enterica and S. bongori

These are subdivided by O and H antigens into serotypes which are named

What is the purpose of slide agglutination is Salmonella identification?

It tells you which serotype is present

How can a serotype be subdivided?

By phage typing

Within phage typing it may be possible to subdivide further by molecular methods - pulse field gel electrophoresis

What are the sources of salmonella?

Live in food animals GIT

In man, large numbers for infective dose

Usually only localised gastroenteritis, rarely systemic infection

S. enteritis PT4 - vertical transmission in poultry from infected adult to egg to chick to infected adult

How is campylobacter caused?

Poultry responsible for most cases

Chickens are carriers

Outbreaks associated with unpasteurised or contaminated milk or untreated water

Gut contents of carriers infects meat at slaughter

What are the characteristics of S. enteritis PT4?

Poultry, eggs

Responsible for pandemic of salmonella food poisoning in 1980s

Can invade oviduct

Interior of eggs contaminated

What is Enterohaemorrhagic E. coli (EHEC)?

Hamburger disease - and others

10-100 bacteria will make you unwell

Can cause shut down of kidneys in children

Describe the reservoir for EHEC

1. Mostly found in intestine of cattle
2. Also found in chickens, deer and pigs
3. Does not make carrier animal sick
4. Meat typically becomes contaminated during the slaughtering process
5. Bacteria on cow's udders and equipment can also contaminate milk

How is botulism caused?

By clostridium botulinum - spore forming bacteria

Endospores germinate in certain food sources

Neurotoxin - most lethal toxin known

* lethal dose: 1.3-2.1 ng/kg

How does the botulinum toxin work?

Absorbed from GI tract, circulated in blood

Acts at neuromuscular junctions of cholinergic nerves and peripheral autonomic synapses

Cleaves proteins involved in synaptic function machinery responsible for exocytic release of neurotransmitter acetylcholine

Flaccid paralysis

What is clostridium perfringens?

Most common type of food-borne illness

C. Perfringens spores in carcase meat

Meat and poultry responsible for at least 90% outbreaks

2/3 of reported outbreaks are in schools, hospitals, factories, restaurants or catering establishments

How does clostridium perfringens work?

Spores resist heating and can germinate if food is inadequately stored

Food allowed to stand at ambient temp for 4 to 24 hours, spores germinate

Food served cold or after desultory re-warming

6 to 12 hours after eating meal, victims complain of crampy abdominal pain and then diarrhoea