Food Microbiology and Foodborne Illness
Pathogen classes
Foodborne illness is caused by infection (Salmonella, Shigella, Campylobacter, E. coli O157:H7, Listeria monocytogenes), intoxication (Staphylococcus aureus enterotoxin, Bacillus cereus emetic toxin, Clostridium botulinum toxin) or toxicoinfection (Clostridium perfringens, B. cereus diarrhoeal type). Viruses such as norovirus and hepatitis A do not grow in food but spread via infected handlers and contaminated water.
Growth and survival
Bacteria need moisture, nutrients, suitable pH and temperature. The danger zone is 5–63°C. Most pathogens grow at pH 4.6–9.0 and water activity above 0.85; spores survive boiling and dry conditions. Listeria grows at refrigeration temperatures; S. aureus toxin and B. cereus emetic toxin are heat-stable, so reheating does not make the food safe.
Worked example
Cooked rice is held at room temperature for six hours, then fried. Several customers vomit within 2–5 hours. Reasoning: the short incubation and vomiting point to B. cereus emetic toxin, formed when cooked rice is cooled slowly; frying kills vegetative cells but not the toxin. The control is rapid cooling and cold holding, not reheating.
Traps
Blaming the last meal eaten; assuming reheating destroys all toxins; ignoring viral contamination because bacteria are the focus; treating spoilage organisms as the only safety indicator.