A microscopic living organism, including bacteria, yeasts, moulds, and viruses, visible only with a microscope. Microbes are central to food for good and ill: beneficial microbes ferment bread, cheese, yoghurt, beer, and wine, while harmful ones cause food spoilage and foodborne disease. A single gram of soil or a drop of contaminated water can contain millions. Food microbiology studies how microbes grow in foods, how processing controls them, and how to harness the useful ones. Modern techniques can identify microbes by their DNA within hours, transforming outbreak investigation. Respect for microbial power underlies every rule of food hygiene.