Human Food Poisoning Flashcards
Identify the main livestock sources of major bacterial foodborne pathogens
- Salmonella enterica - meat, eggs, raw milk, faecally contaminated fruit/ veg
- E coli - Beef, raw milk, faecally contaminated F and V
- Campylobacter - poultry meat and others
Listeria monocytogenes - cooked meat, soft cheese, smoked fish - Clostridium - Poorly stored cooked meat
- Hepatitis E - pork and pork products
- Norovirus - seafood
What is food security?
when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food which meets their dietary needs and food preferences for an active and healthy life
Campylobacter
- The most common worldwide cause of human bacterial gastroenteritis
- Most disease caused by 2 species: Campylobacter jejuni (90% cases) & Campylobacter coli
- Tends to cause sporadic cases rather than outbreaks
- Biology poorly understood
- Causes more than 500,000 cases each year in the UK
- Gram negative spiral rods
- Onset of disease symptoms usually occurs two to five days after infection with the bacteria, but can range from one to ten days.
- The most common clinical symptoms of Campylobacter infections include diarrhoea (frequently with blood in the faeces), abdominal pain, fever, headache, nausea, and/or vomiting. The symptoms typically last three to six days.
- Long term sequelae including neurological problems such as Guillain-Barre syndrome
- Infection in developing countries associated with more watery diarrhoea-more akin to cholera
Who are most at rick to campylobacter infection?
- Under 5’s
- Over 65’s – immune system compromises
- Bowel Cancer patients
- Those taking proton-pump inhibitor drugs (increased gastric pH) – omeprazole
What is the main source of human campylobacter?
poultry meat is the source for 60-70%
Red meat and water other main
control campylobacter -
sampling and microbiology
Ultimately it is possible to rear Campylobacter-free chickens but they would cost about
£20-50 per bird
E coli and human enteric disease
• Several pathotypes associated with
enteric infections
• Most EHEC/STEC strains colonise the GI tract of cattle, sheep and goats without disease
• Prevalence of faecal shedding believed to be around 5% of cattle in UK, more than 25% in USA
• Some strains cause diarrhoea in calves and oedema in pigs
• The distal rectum is the main site of colonisation and requires the LEE T3SS and other factors to colonise
• Even if not shed, bacteria from the GI tract may contaminate meat at time of slaughter
• Many human cases linked to poorly cooked ground/minced beef (hamburger disease) or cross contamination of cooked meats from raw infected meat
Yersinia and Shigella
- Both Enterobacteriacae-similar to Salmonella & E .coli (and also utilise T3SS)
- Yersinia enterolitica causes foodborne yersiniosis (common worldwide)
- 4 species of Shigella (flexneri, boydii, sonnei, dysentriae) causing human dysentry
- Shigella can be transmitted by foodborne or person-to-person routes
- Shiga toxins are produced by some species
- Not so common in the UK
Listeria monocytogenes
- Gram positive rod-shaped intramacrophage pathogen
- May be zoonotic (including foodborne)
- Associated with cooked meats, pate, soft cheese, smoked fish, pre-prepared sandwiches and cook-chill meals
- Can grow well at low temperatures-so particular risk (colonise on cooked chilled food – multiply – cause disease)
Human listeriosis
- Most cases are mild, either gastroenteritis or flu-like symptoms
- Pregnant women, the elderly and immunocompromised at particular risk
- Systemic (septicaemia) and CNS infections (meningitis) have recently increased in prevalence in the UK
- Systemic infection of the 60+ age group a particular problem
- Around 100-200 cases in England & Wales annually (higher in France where people eat more cheeses etc)
- Non-pregnancy associated infection has mortality rate in excess of 30%
Bacterial toxins
- Exotoxins produced by a range of bacteria cause food poisoning
- Enterotoxins usually induce diarrhoea, emetic toxins vomiting
- Staphylococcus aureus produced 5 different enterotoxins
- Sporadic outbreaks of Staphylococcus aureus food poisoning caused usually by poor food handling
- Other toxins associated with milk products
Bacillus food poisoning:
- Bacillus cereus (and to a lesser extent B. subtilis) is a Gram positive spore forming rod
- Produces two toxins which are heat stable survive being cooked
- Associated with pulses and rice (though any food may be affected)
Bacillus pathogenesis:
- Vegetative cells killed by cooking spores are not
- If cooked rice/pulses are not chilled, spores can germinate, bacteria grows and toxins produced (e.g. left on the side in the kitchen)
- Toxins are not destroyed by re-heating
- Consumption-e.g. Fried rice leads to exposure to toxins
- Emetic toxin induces rapid and profuse vomitting (around 15 minutes after consumption)
- Enteric toxin induces profuse, painful but short-lived diarrhoea (4-6 hours after consumption)
Clostridium poisoning:
- Clostridium is a genus of Gram positive spore forming rods assocsited with a number of diseases
- Clostridium perfringens and C. botulinum may cause severe food poisoning
- Clostridium difficille (usually a part of gut flora) may cause diarrhoea following antimicrobial chemotherapy-disruption of normal flora
- C. difficille is frequently resistant and a major nosocomial problem
C. botulinum:
- Spores are found in a variety of environments
- Typically foodborne form caused by poorly canned, bottled foods or in honey
- Germinating spores lead to formation of vegetative cells that release a potent toxin
- Toxin acts to block nerve synapsis causing paralysis and death
- Major scares in 1970s from tinned salmon and corned beef canned foods
