MadSci Network: Microbiology

Re: E. Coli normally found in colon -- so why dangerous?

Date: Wed Sep 15 20:13:54 1999
Posted By: Dr. Richard J. Obiso, Jr., Faculty, MICROBIOLOGY AND Biochemistry, East Tennessee State Univ.
Area of science: Microbiology
ID: 937309491.Mi

Most E. coli are "normal flora" bacteria. These bacteria live in our intestines at about 100,000,000 bacteria per gram of intestinal matter - - so there are a lot in our intestines. Before the early 1960's no one had ever heard of a "bad" E. coli. But, from evolution and horizonal transfer of DNA, several E. coli "picked up" toxin genes. These toxin genes caused the E. coli to become pathogens. These bacteria are still E. coli, but they are now armed with toxin genes that can damage tissues, cause diarrhea, and even kill people.

The way that these E. coli pick up toxin genes is by being infected with a virus. There are bacterial viruses (they do not affect humans) that can give these E. coli the DNA for toxin genes. These genes make the E. coli toxigenic. Now there are several types of Toxigenic E. coli - - STEC, ETEC, EHEC, EAEC, and others.

I hope this answers your question.
-Rik Obiso
Richard J. Obiso, Jr., Ph.D.
Assistant Professor
East Tennessee State University

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