Food Safety: The Bacteria You Need to Know

Salmonella is found primarily in raw poultry, eggs, and unpasteurised dairy. It can survive on surfaces for hours and is destroyed at 74°C (165°F). Illness begins 6–72 hours after exposure and causes diarrhoea, fever, and abdominal cramps lasting 4–7 days. Roughly 1.35 million infections occur in the US annually.

Campylobacter is the most common bacterial cause of food poisoning in most high-income countries. It lives in the gut of poultry and is often spread through raw chicken juices. Critically, it has an extremely low infectious dose — fewer than 500 organisms can cause illness. It is destroyed at the same temperature as Salmonella but is uniquely vulnerable to freezing and drying.

E. coli O157:H7 is found in beef (particularly ground beef), unpasteurised milk, and contaminated leafy greens. It produces Shiga toxin and can cause haemolytic uraemic syndrome (HUS), a serious kidney complication, particularly in children under 5 and elderly people. Ground beef must reach 71°C (160°F) because grinding distributes surface bacteria throughout the meat.

Listeria monocytogenes is unusual because it can grow at refrigerator temperatures (as low as 0°C). It is particularly dangerous for pregnant women (50× higher risk), immunocompromised individuals, and elderly people. It is found in soft cheeses, deli meats, smoked fish, and unpasteurised dairy. It is killed by cooking but the risk from ready-to-eat foods is significant.

Temperature is the most reliable safety variable you can control. A calibrated instant-read thermometer removes all guesswork and should be considered essential kitchen equipment — they cost under $20.

Insert the thermometer into the thickest part of the food, away from bone and fat, which conduct heat differently. For whole poultry, check the thickest part of the thigh. For stuffed items, check the stuffing as well.

• Whole poultry (chicken, turkey): 74°C / 165°F
• Ground meat (beef, pork, lamb): 71°C / 160°F
• Whole cuts of beef, pork, lamb: 63°C / 145°F + 3 min rest
• Fish and shellfish: 63°C / 145°F (flesh should be opaque and flake)
• Eggs: cook until yolk and white are firm, or 71°C for dishes
• Leftovers and casseroles: 74°C / 165°F
• Ham (uncooked): 63°C / 145°F + 3 min rest

Bacteria multiply most rapidly between 4°C and 60°C (40°F–140°F) — called the temperature danger zone. At 37°C (body temperature), many bacteria double every 20 minutes. Food left in this range for 2 hours or more enters high-risk territory. In hot weather (above 32°C), that window shrinks to 1 hour.

The 2-hour rule applies to total cumulative time, not a single exposure. If food sat out for 30 minutes before being refrigerated and is then left out again, the clock continues from 30 minutes.

Refrigerators should be set to 4°C or below. Freezers should be at or below -18°C. Use a refrigerator thermometer — the built-in dial controls are notoriously unreliable. The back of the refrigerator is coldest; the door shelves are warmest and should only store condiments.

Cross-contamination occurs when bacteria from raw food transfer to ready-to-eat food via hands, surfaces, or utensils. This is responsible for a large proportion of foodborne illness because the contaminated food is eaten without further cooking to kill the bacteria.

The most high-risk scenario is cutting raw chicken on a board and then using the same board — even after a quick rinse — to cut vegetables or bread. Campylobacter survives brief cold water rinsing. Always wash boards with hot water and soap, or better, keep dedicated boards for raw meat.

Hands are the most common vector. Wash hands with soap for 20 seconds after handling raw meat, poultry, eggs, or unwashed produce — and before touching anything else in the kitchen. A rinse under cold water without soap is ineffective.

• Separate boards: one for raw meat, one for produce/cooked food
• Never rinse raw chicken — splash spreads bacteria up to 1 metre
• Wash hands 20 seconds with soap after all raw protein handling
• Change or sanitise cloths and sponges regularly — they harbour bacteria
• Store raw meat on the lowest fridge shelf to prevent drip contamination
• Use separate utensils for raw and cooked meat on the grill

Cooked food must move through the danger zone quickly. Large pots of soup, stew, or rice should not cool on the counter for hours before refrigerating. Divide into shallow containers (less than 7cm deep) to accelerate cooling, or place the pot in a sink of cold water with ice, stirring frequently.

The goal is to get food below 21°C within 2 hours and below 4°C within 4 hours total. Most cooked food is safe in the refrigerator for 3–4 days. Cooked poultry and seafood are best consumed within 2–3 days.

Rice deserves special mention. Bacillus cereus is a spore-forming bacterium naturally present on rice. Spores survive cooking, and if cooked rice is left at room temperature, the spores germinate and produce a heat-stable toxin that reheating cannot destroy. Cook rice fresh, or cool and refrigerate within 1 hour of cooking.

Myth: 'Rinsing raw chicken removes bacteria.' Reality: rinsing raw chicken spreads bacteria to surrounding surfaces via water splash — it does not reduce bacteria on the chicken. Cooking to 74°C is the only reliable method.

Myth: 'You can tell if food is safe by smell or colour.' Reality: the bacteria that cause foodborne illness generally do not produce noticeable odour, colour, or texture changes. Food that smells fine can still cause serious illness.

Myth: 'Marinating meat at room temperature is fine.' Reality: meat should always be marinated in the refrigerator. Even a few hours at room temperature gives bacteria time to multiply to dangerous levels.

Myth: 'Five-second rule.' Reality: bacteria transfer is essentially instantaneous on contact with a surface. Moist foods pick up more bacteria than dry ones, but time on the floor is not a reliable safety indicator.