Microbiology & Food Contamination

Which bacterium is commonly associated with raw poultry and causes gastroenteritis?

• AListeria monocytogenes
• BCampylobacter jejuni✓
• CSalmonella typhi
• DClostridium perfringens

Answer: Campylobacter jejuni is the most common cause of bacterial gastroenteritis in developed countries. It's primarily found in raw or undercooked poultry and can survive in cooled foods.

What is the typical incubation period for Salmonella food poisoning?

• A6-12 hours
• B12-36 hours✓
• C2-5 days
• D7-14 days

Answer: Salmonella typically has an incubation period of 12-36 hours (range 6-72 hours). Symptoms include diarrhea, abdominal cramps, fever, and vomiting lasting 4-7 days.

Which bacterium produces a heat-resistant spore and can survive cooking temperatures?

• AE. coli
• BSalmonella
• CClostridium perfringens✓
• DStaphylococcus aureus

Answer: Clostridium perfringens produces spores that can survive cooking. This is why cooling food rapidly and reheating to 70°C for 2 minutes (or 75°C for 30 seconds) is critical to kill vegetative cells.

What is the primary source of Listeria monocytogenes in food?

• APoultry and eggs
• BSoft cheeses, ready-to-eat meat products, and chilled foods✓
• CShellfish only
• DBeef products

Answer: Listeria monocytogenes is found in soft cheeses (especially unpasteurized), deli meats, pates, and chilled ready-to-eat foods. It can grow at refrigeration temperatures, making it particularly hazardous.

Which pathogenic E. coli strain is a major cause of serious food-borne illness?

• AE. coli O145
• BE. coli O157:H7✓
• CE. coli O26
• DE. coli O111

Answer: E. coli O157:H7 produces Shiga toxin and can cause severe hemolytic uremic syndrome (HUS), particularly in children. It's found in undercooked beef and contaminated produce.

How do bacteria reproduce under ideal conditions?

• AAsexually, one cell divides into two✓
• BSexually with genetic exchange
• CBy budding like yeast
• DThey don't reproduce, they just grow

Answer: Bacteria reproduce by binary fission (asexual reproduction). Under ideal conditions (proper temperature, pH, moisture), they can double in number every 20 minutes.

What is the 'danger zone' for bacterial growth in food?

• A0-8°C
• B8-15°C
• C8-63°C (or 46-145°F)✓
• D63-100°C

Answer: The danger zone is 8-63°C (46-145°F). Bacteria grow rapidly in this temperature range. Food should not be left in the danger zone for more than 2 hours (1 hour if above 32°C).

What are the FOUR main conditions bacteria need to grow?

• ALight, heat, salt, sugar
• BFood, water, warmth (temperature), time✓
• CAir, moisture, enzymes, bacteria
• DpH, salt, meat, vegetables

Answer: Bacteria need: Food (organic material), Water (moisture), Warmth (optimal around 37°C), and Time. Remove any of these and bacterial growth is inhibited. Remember 'FWWT'.

What does 'cross-contamination' mean in food safety?

• AFood that is slightly contaminated
• BTransfer of harmful bacteria from one food to another or from non-food surfaces to food✓
• CMixing raw and cooked foods together
• DFood that is contaminated twice

Answer: Cross-contamination is the transfer of pathogenic bacteria (usually from raw to cooked food, or from surfaces to food). It's a major cause of food-borne illness and is preventable through hygiene.

What is a 'ready-to-eat' food?

• AAny food that can be eaten
• BFood that will not be cooked or reheated before consumption✓
• CFood served in a restaurant
• DCanned food

Answer: Ready-to-eat foods are consumed as-is without further cooking. They include deli meats, salads, cooked chicken, soft cheeses. They require strict hygiene to prevent contamination.

Why are raw vegetables potentially hazardous?

• AThey always contain bacteria
• BThey may be contaminated with pathogens during growth (soil, water, animal contact) or processing✓
• CThey cannot be safe if eaten raw
• DVitamins turn to toxins in raw form

Answer: Raw vegetables can be contaminated during growth (soil-borne pathogens like E. coli O157, Listeria) or during washing/processing. Leafy greens are particularly high-risk.

What is the maximum temperature at which food can be left in storage for safety?

• ARoom temperature (20°C)
• B8°C or below for chilled foods✓
• C15°C for ambient storage
• D-5°C for all foods

Answer: Chilled foods should be stored at 8°C or below to prevent pathogenic growth. Different foods have specific requirements (eggs 8°C, cooked meats 3-4°C), but 8°C is the general guideline.