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.