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What causes the most cases of food poisoning: viruses, bacteria, fungi or parasites?
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
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
The presence of faecal organisms (E.coli) in a sample indicates ...?
a need for further investigation
What type of machine can be used to count the particles present in milk?
What test forms the basis of international agreements and standards (legislation)?
Total viable counts (TVC)
Which of the following can multiply in foods? Viruses, bacteria, fungi, parasites
Bacteria and fungi can multiply in foods
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
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
What colour are Salmonella colonies? What does Salmonella produce that makes food smell bad?
What colour is Campylobacter on black medium?
What colour is E.coli on MacConkey agar? And MUG agar?
- MacConkey - colourless
- MUG - glowing colonies
Is Clostridium perfringes aerobic or anaerobic?
Where is Clostridium perfringes found?
In animal guts, faeces contaminate the carcase at slaughter
What do sporulating strains of Clostridium perfringes produce?
What does Clostridium perfringes look like on blood agar?
It is haemolytic
Where is Staphylococci found?
On chicken skin and in chicken tissue. Also found in milk products, cheese and creams.
Baird-Parker agar is highly selective for what strain of Staphylococcus?
Is staphylococcus aureus coagulase positive or negative?
Listeria can be grown using cold enrichment, what does this mean?
Listeria can grow at 4°C but other bacteria cannot
What must be present in Listeria for it to be pathogenic?
The listerolysin gene
Is listeria haemolytic on blood agar?
Is Clostridium botulinum aerobic or anaerobic?
Where is clostridium botulinum found?
Normally associated with home grown foods put in cans/jars. Occasionally found in meat.
What does clostridium botulinum cause?
Flaccid paralysis - fatal if it paralyses your respiratory muscles
Where is Yersinia enterocolitica found?
Pigmeat, venison, pheasant and salads
Can Yersina be grown using cold enrichment?
List some methods used to monitor bacteria in food
- Demonstration of presence of bacteria
- Stained smears
- Fluorescent antibody
- Metabolic detection eg ATP detection
What are indicators of bacterial infection?
- Presence of acute phase proteins
- Cytokine detection
- Demonstration of past presence
- Antibody detection
What are other counting methods?
- Particle counting as Bactoscan for milk
- Luciferase-linked probes
- Immunomagnetic methods
- Genome size calculations
- Taqman real time PCR