E. coli K12, the prokaryotic wimp

    Escherichia coli is a gram-negative bacterium that is a normal component of the human intestinal flora, and is ordinarily not a dangerous organism. The K12 and related strains of E. coli used in molecular cloning have been modified so that they are able to survive in culture only under very specific conditions, and are unable to survive at all in the human gut. 

    Municipal water sources are routinely tested for the presence of "coliform" (rod-shaped) bacteria like E. coli, which would indicate possible contamination with human or animal fecal material. Recent cases of E. coli contamination stem from "natural" pathogenic strains of E. coli that have found their way into public water sources through improper sterilization or filtration.

Figure © 1991 by Gonick & Wheelis, The Cartoon Guide to Genetics; text © 2014 by Steven M. Carr