Food-borne Infections and Toxins Flashcards
What is food poisoning?
Food-borne infections in humans due to bacterial toxins in food leading to diarrhoea and vomiting which is occasionally severe or fatal
What is the best way to make sure you don’t get food poisoning?
Cook your food properly
What are the five main agents of concern?
Campylobacter - 60% of cases Salmonella - 5 % of cases Listeria - highest number of deaths E. coli Norovirus - 35% of cases
What are some other kinds of food borne illness?
Staph aureus (nasal secretions) Bacillus cereus (rice) Clostridium perfringens Type A (faeces) Clostridium botulinum (soil and faeces) Vibrio parahaemolyticus (shellfish)
What are the characteristics of Campylobacter species?
Curved gram negative rod
Microaerophilic at 42C
Endemic in animals, carried by birds and many mammals
Which species of Campylobacter cause food poisoning?
C. jejuni from poultry
C. coli from pigs
What is the pathogenesis of Campylobacter food poisoning?
Incubation period of 2-5 days
Colonises small intestine and causes enteritis
Diarrhoea, stomach pains, cramps, fever
Eat contaminated food to become infected
How is Campylobacter diagnosed?
Faecal culture on blood agar with antibiotic selection for 48 hours at 42C in microaerophilic atmosphere
How can Campylobacter food poisoning be prevented?
Cook food
What makes Listeria different from other food poisoning bacteria?
Can grow at t stop it
What is the source of infection for humans with Listeriosis?
Contaminated raw meat
Unpasteurised milk
Cheese made using unpasteurised milk
Foods containing raw vegetables
Why is Listeria so virulent?
Invades the cell, escapes from the phagosome, replicates in the cytosol and spreads between cells directly
Which groups of people are most at risk from Listeria?
Immunocompromised individuals
The young
The elderly
Pregnant women
How can Listeriosis be prevented?
Cooking
Proper refrigeration
What are the characteristics of Norovirus?
Calicivirus
Small infective dose
Resistant in the environment
Spread person to person or in foods or faeces
What are the characteristics of E. coli O157?
Aka STEC
Shiga like toxin produced (ST-1 and ST-2)
What is the public health significance of STEC?
Carriage by calves -> beef animals -> contaminated meat -> cooked foods
Very low dose (10 CFU) needed to cause infection in humans
What are the clinical signs of STEC infection?
Haemorrhagic colitis and Haemolyti Uraemic syndrome causing renal failure
What is the pathogenesis of STEC?
Attaches and effacing lesions in the gut caused by Intimin
Shiga like toxin is absorbed causing vascular damage, oedema and thrombi leading to thrombotic thrombocytopaenis purpurea
How is STEC diagnosed?
Culture and Latex agglutination test
What are the characteristics of Salmonella?
Many animals carry small numbers, infectious dose high
Vaccination programmes in poultry
Human salmonellosis originates from animal faeces on food/farms
How is salmonellosis diagnosed?
Culture of faeces on enriched agar -> selective culture -> bochemical profile -> serotyping O and H antigens
How does Staph aureus cause food poisoning?
From nasal secretions of food handlers
30% of strain produce an enterotoxin
How does Bacillus cereus cause food poisoning?
Cooking rice activates spores, toxin produced on rice, eaten as reheated or fried rice
How does C. perfringens cause food poisoning?
5% of strains produce enterotoxin (CPE)
Contaminated food stuffs, incubated anaerobically, released on sporulation
How does C. botulinum cause food poisoning?
Botulinum toxin in heated anaerobic foods (canned/bottled)
