Any small organism viewed only with a microscope could be categorized as a microorganism or microbe. In food, the microorganisms of concern are bacteria, yeasts and molds, although viruses and parasites are also important 2 . Bacteria are single celled and rod, spherical or ovoid in shape. Some species of bacteria also produce spores, some of which are resistant to heat and chemicals 3 .
Yeasts are also usually one cell, but they are larger than bacteria.
Molds are multicellular microorganisms that grow by producing thread-like mycelial filaments 3 . They are more likely to grow on food stuffs such as breads, nuts, and cheeses that are low in moisture content. They are widely distributed in our environment. Some common living places of microbes are air, water, soil, plants, animals, human beings, sewage, fertilizer, food ingredients, processing equipment, and packaging materials. The microbes found in food include those associated with the raw material, those acquired during harvesting, handling, and processing, and those surviving any preservation treatment and storage 1 .