WSQ Food-borne Pathogens 2 — Questions and Answers
Question 1: What is the difference between food infection and food intoxication?
- They are the same thing
- Food infection is caused by consuming live pathogens that multiply in the body; food intoxication is caused by consuming toxins already produced by bacteria in the food (Correct answer)
- Infection is more serious
- Intoxication only comes from chemicals
Correct answer: Food infection is caused by consuming live pathogens that multiply in the body; food intoxication is caused by consuming toxins already produced by bacteria in the food
Infection (e.g., Salmonella) occurs when you ingest live bacteria that grow in your body. Intoxication (e.g., Staphylococcus toxins) occurs when you eat pre-formed toxins — cooking kills the bacteria but not the toxins.
Question 2: Which of the following foods are considered 'potentially hazardous' (high-risk) in Singapore?
- Only raw meat
- Cooked rice, meat, poultry, seafood, dairy products, cut fruits, cooked vegetables, and tofu — foods that are moist, protein-rich, and pH neutral (Correct answer)
- Only dairy products
- Only imported foods
Correct answer: Cooked rice, meat, poultry, seafood, dairy products, cut fruits, cooked vegetables, and tofu — foods that are moist, protein-rich, and pH neutral
Potentially hazardous foods are those that support rapid bacterial growth: protein-rich, moist, and near-neutral pH. In Singapore, cooked rice is a notable high-risk food due to Bacillus cereus.
Question 3: What is Bacillus cereus and why is it particularly relevant to rice in Singapore?
- A virus found in water
- A spore-forming bacterium commonly found in rice that produces toxins if cooked rice is not stored properly; the spores survive cooking (Correct answer)
- A chemical in rice
- A type of fungus
Correct answer: A spore-forming bacterium commonly found in rice that produces toxins if cooked rice is not stored properly; the spores survive cooking
Bacillus cereus spores survive cooking. If cooked rice is left at room temperature (common in Singapore hawker centres), the spores germinate and produce toxins that cause vomiting or diarrhoea.
Question 4: What is 'bio-film' and how does it relate to food safety?
- A documentary about biology
- A slimy layer of bacteria that adheres to surfaces (cutting boards, pipes, equipment), protecting bacteria from cleaning and sanitising agents (Correct answer)
- A biodegradable food wrap
- A type of food preservative
Correct answer: A slimy layer of bacteria that adheres to surfaces (cutting boards, pipes, equipment), protecting bacteria from cleaning and sanitising agents
Biofilms are colonies of bacteria that form a protective matrix on surfaces. They are resistant to normal cleaning and require thorough scrubbing and proper sanitisation to remove.
Question 5: How does pH affect bacterial growth in food?
- pH has no effect on bacteria
- Most pathogenic bacteria grow best at pH 4.6-7.5 (near neutral); highly acidic foods (pH below 4.6) inhibit bacterial growth (Correct answer)
- Bacteria only grow in acidic foods
- Bacteria prefer very alkaline foods
Correct answer: Most pathogenic bacteria grow best at pH 4.6-7.5 (near neutral); highly acidic foods (pH below 4.6) inhibit bacterial growth
Most dangerous bacteria thrive at pH levels between 4.6 and 7.5. This is why acidic foods (pickles, citrus) and acidified foods are less likely to cause food-borne illness.
Question 6: What are indicator organisms in food safety testing?
- Organisms that indicate the food is safe
- Organisms like E. coli and coliforms whose presence in food indicates possible faecal contamination or general hygiene failures (Correct answer)
- Only visible organisms like mould
- Organisms added to food for testing
Correct answer: Organisms like E. coli and coliforms whose presence in food indicates possible faecal contamination or general hygiene failures
Indicator organisms like E. coli suggest faecal contamination, while total coliform counts indicate general hygiene levels. Their presence does not necessarily mean pathogens are present but signals a hygiene problem.
WSQ Food-borne Pathogens 2
What is the difference between food infection and food intoxication?