Escherichia coli is an Enterobacteria described by Bergey's Manual (1957). Escherichia is a Gram-negative rod which can be motile by peritrichous flagella or nonmotile. Escherichia is also a facultative anaerobe which has both a respiratory and a fermentative type of metabolism, and commonly occurs in the intestinal tract of humans and other animals. The strain E. coli K-12 is a debilitated strain which does not normally colonize the human intestine. It has also been shown to survive poorly in the environment, has a history of safe commercial use, and is not known to have adverse effects on microorganisms or plants.

Because of its wide use as a model organism in research in microbial genetics and physiology, and its use in industrial applications, E. coli K-12 is one of the most extensively studied microorganisms. As a result, these K-12 strains are well-characterized and should be expected to remain as pure cultures under standard microbiological practices. K-12 strains are distinguishable from other Escherichia.

According to the Final Risk Assessment of the U.S. Environmental Protection Agency (EPA) (1997) , a potential hazard of Escherichia coli K-12 and its derivative strains to human health should be addressed in terms of its potential to colonize the human intestinal tract and the production of a toxin. In this assessment, it was determined that E. coli K-12 does not pose a threat to human or animal health in terms of colonization; any concerns can be discarded because of this kind of bacteria’s poor ability to survive and mobilize plasmids ( to the native intestinal flora in murine models and even humans (Levy and Marshall, 1980).