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What causes the most cases of food poisoning: viruses, bacteria, fungi or parasites?
Bacteria
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Give four reasons for foods to be sampled?
- Checks on hygienic production and handling techniques
- Quality control and shelf life performance
- Suspicion of being the cause of food poisoning or as a result of consumer complaint
- Verification of the quality of imported food
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List some microbiological tests carried out on food
- Total viable count
- Counts of coliforms
- Counts of pyschotrophs
- Presence of pathogens
- Presence of bacterial toxins
- Presence of fungi
- Presence of mycotoxins
- Indicator organisms - E.coli, enterococci
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The presence of faecal organisms (E.coli) in a sample indicates ...?
a need for further investigation
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What type of machine can be used to count the particles present in milk?
Bactoscan
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What test forms the basis of international agreements and standards (legislation)?
Total viable counts (TVC)
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Which of the following can multiply in foods? Viruses, bacteria, fungi, parasites
Bacteria and fungi can multiply in foods
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List the bacterial pathogens present in foods
Salmonella, campylobacter, E.coli O157, Clostridium perfringens, Staphylococci, Listeria monocytogenes, Clostridium botulinum, Yersinia enterocolitica, Aeromonas hydrophila/sobria/caviae
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Why might we need to recover damaged organisms before putting samples in selective broth/agar?
As they might have been damaged by heat, storage, chilling, disinfectants and preservatives
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What colour are Salmonella colonies? What does Salmonella produce that makes food smell bad?
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What colour is Campylobacter on black medium?
Grey
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What colour is E.coli on MacConkey agar? And MUG agar?
- MacConkey - colourless
- MUG - glowing colonies
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Is Clostridium perfringes aerobic or anaerobic?
Anaerobic
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Where is Clostridium perfringes found?
In animal guts, faeces contaminate the carcase at slaughter
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What do sporulating strains of Clostridium perfringes produce?
Enterotoxin
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What does Clostridium perfringes look like on blood agar?
It is haemolytic
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Where is Staphylococci found?
On chicken skin and in chicken tissue. Also found in milk products, cheese and creams.
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Baird-Parker agar is highly selective for what strain of Staphylococcus?
Staphylococcus aureus
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Is staphylococcus aureus coagulase positive or negative?
Coagulase positive
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Listeria can be grown using cold enrichment, what does this mean?
Listeria can grow at 4°C but other bacteria cannot
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What must be present in Listeria for it to be pathogenic?
The listerolysin gene
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Is listeria haemolytic on blood agar?
Yes
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Is Clostridium botulinum aerobic or anaerobic?
Anaerobic
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Where is clostridium botulinum found?
Normally associated with home grown foods put in cans/jars. Occasionally found in meat.
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What does clostridium botulinum cause?
Flaccid paralysis - fatal if it paralyses your respiratory muscles
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Where is Yersinia enterocolitica found?
Pigmeat, venison, pheasant and salads
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Can Yersina be grown using cold enrichment?
Yes
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List some methods used to monitor bacteria in food
- Demonstration of presence of bacteria
- Stained smears
- Probes
- Fluorescent antibody
- PCR
- Culture
- Metabolic detection eg ATP detection
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What are indicators of bacterial infection?
- Presence of acute phase proteins
- Cytokine detection
- Demonstration of past presence
- Antibody detection
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What are other counting methods?
- Particle counting as Bactoscan for milk
- Luciferase-linked probes
- Immunomagnetic methods
- Genome size calculations
- Taqman real time PCR
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