Foodborne Microorganisms and Major Allergens
Match the organism to its vehicle
Most outbreaks are bacterial, but viruses and parasites are tested too. Learn each pathogen by its usual food vehicle and its temperature behavior.
Spore-formers survive normal cooking. Clostridium perfringens thrives in stews, gravies, and reheated meat; Bacillus cereus in cooked rice and pasta. Salmonella comes from poultry, eggs, and produce. E. coli O157:H7 is linked to ground beef and raw produce. Listeria monocytogenes grows at refrigeration temperatures, so it threatens ready-to-eat deli meat, soft cheese, and smoked seafood. Staphylococcus aureus lives on skin and in wounds and produces a toxin that heat cannot destroy. Vibrio comes from shellfish; Shigella from produce and water.
Norovirus and hepatitis A do not reproduce in food but need very few particles. Norovirus is the leading cause of foodborne illness, spread by hands and by shellfish and RTE foods; hepatitis A spreads the same way and can cause jaundice.
FAT TOM: Food, Acidity, Temperature, Time, Oxygen, Moisture. TCS foods support growth and must stay out of the danger zone (41F to 135F).
Allergens
The nine major allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, sesame. Reactions can be fatal from trace amounts. Cross-contact is the transfer of allergen protein, not bacteria: shared fryer oil, tongs, or a cutting board. Controls are handwashing, dedicated equipment, label reading, and accurate description of dishes.
Traps
- Toxin-mediated illness (S. aureus, B. cereus) is not fixed by reheating.
- Listeria is the answer when the clue is 'grows in the cooler.'
- There is no safe threshold for an allergen; a crumb counts.
Rule of thumb: match the vehicle. Fried rice means B. cereus. Gravy means C. perfringens. Ground beef means E. coli.