The Survival of Malidixic Acid Resistance Genetic Marker of Escherichia Coli x1776 through the Gastrointestinal Tract of Mice

Abstract

Escherichia coli x17?6, a strain created from Escherichia coli K12, is used as an EK2 host (17) in plasmid engineering experiments. It is unable to survive passage through the intestinal tracts of rats at frequencies of less than 10-11 bacteria per milliliter because of several mutations that cause sensitivity to bile and requirements for diamino­ pimelic acid (DAP) and thymine (15). Although DNA degradation accompanies thymine-less death in in vitro experiments and is an all-or-none response for any given cell (15), it is likely that lysis associated with DAP-less death may liberate DNA prior to its degradation. Since undegraded recombinant DNA might be taken up by robust microorganisms encountered in the natural environment, especially in the intestinal tracts of humans after inadvertant ingestion by laboratory workers, by the mechanism of transformation, or as a consequence of con­comitant phage infection, it is important to determine the "survival potential" of such DNA in non-laboratory controlled environments.