Microorganisms and Causes of Foodborne Illness
Types of microorganisms
Bacteria, viruses, parasites and fungi (moulds and yeasts) can be in food. Only some cause illness; others spoil food. Spoilage organisms may make food slimy or sour, but pathogens can be present with no visible change. Bacteria usually need food, moisture, warmth, time, appropriate acidity and, for many, oxygen; this is often summarized as FATTOM. Viruses such as norovirus and hepatitis A do not multiply in food-they need a living host-but a small number can make someone ill. Parasites are often linked to raw or undercooked meat, fish or contaminated water.
Infection, intoxication and toxins
An infection occurs when live microorganisms grow in the body. An intoxication occurs when a toxin already in the food causes illness. Some toxins are heat-stable, so reheating or cooking will not make the food safe. Spores can survive cooking and then germinate if food is cooled slowly or held warm.
Traps
Common traps: freezing kills all bacteria (false); viruses multiply in food (false); all bacteria are harmful (false); food with a bad smell is the only unsafe food (false). Another trap is assuming cooking always destroys toxins. Also, Bacillus cereus is associated with cooked rice that is cooled slowly or held at room temperature.
Worked example
Cooked rice is left in a warm kitchen overnight. Reheating it does not make it safe because the toxin may already be present. Discard it. Rule of thumb: keep high-risk food out of 4–60°C and cool it quickly.