What are bacteria?

By Susan Brewer, Ph.D., University of Illinois,
Department of Food Science and Human Nutrition

Bacteria, single-celled organisms that come in a myriad of shapes and sizes, are everywhere—in the soil, air, water, and even the foods we eat.  Some grow when oxygen is available; some grow only when there is none.  Some grow only in acid foods; some can’t tolerate acid. Some grow best at cold temperatures; some grow best at warm temperatures.  Some produce spores, like seeds, so they can tolerate adverse conditions.  Many do not.  Some invade the body, producing infections.  Some produce toxins in the food as they grow, and the toxins make us sick.  In general, bacteria need nutrients (foods), moisture, favorable temperatures, and gas atmospheres to thrive, to grow to a sufficient number to spoil food or make us sick.
FDA, 2008. Bad Bug Book. “Foodborne Pathogenic Microorganisms and Natural Toxins Handbook.”
Kendall, P. 2008.  “Bacterial food-borne illness.”  Cooperative Extension Service. Colorado State University, Fort Collins, CO.  Fact sheet No. 9.300.
Jay, J.M. 2000. Modern Food Microbiology. Gaithersburg, MD: Aspen Publishers.


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