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Public Reseachers Complete Sequence for Deadly E. Coli Strain

WASHINGTON, Jan 25 - The National Institute of Allergy and Infectious Diseases has announced the sequencing of a strain of Escherichia coli bacteria responsible for deadly outbreaks of food poisoning. The results of the project will be published Thursday in Nature .

The sequence was completed using the shotgun approach, which the publicly funded Human Genome Project previously insisted was inferior to its BAC-based method.

“The automated sequencers are more robust and use smaller scale samples and multiple channels at once,” said Dennis Lang, enteric diseases program officer at NIAID. Lang said his program has been using shotgun sequencing for the last three to four years. Public researchers have also previously said that they would use the shotgun approach to sequence the mouse.

Researchers also used the optical mapping, a technique for assembling and confirming DNA sequences that was invented by the paper’s co-author David Schwartz of the Genome Center at the University of Wisconsin-Madison. In this technique, specially-prepared individual DNA molecules are photographed and measured using a fluorescence microscope.

Of the more than 5,000 genes in this pathogen, about 20 percent were not present in a harmless laboratory strain of E. coli . These new genes may give the disease-causing bacteria the ability to withstand the body's fever and produce more toxins.

Bacteria have several ways to pick up new genetic material, and E. coli seems to be particularly good at it. They shuffle their genes by exchanging DNA directly or via infection with viruses called bacteriophages that can acquire genetic material from one type of bacteria and insert it in the DNA of another. One of the reasons E. coli food poisoning is so difficult to treat is that the antibiotics that kill the bacteria also may stimulate the growth of the viruses and the release of their toxins.  

The new sequence information will give researchers a much larger set of markers they can use to try to detect the dangerous strain when it appears in food or in the human body. In addition, it will advance work toward an animal vaccine against the bacteria, which would help prevent it from getting into the human food supply.

Foodborne illness caused by the " O157:H7" strain of E. coli is a worldwide public health problem, especially threatening to children and the elderly. About 75,000 infections from contaminated food occur each year in the United States alone. E. coli O157:H7 was first identified during a highly publicized 1982 outbreak linked to contaminated hamburger meat.

" E. coli O157:H7 is one of the most dangerous pathogens threatening our food and water supplies," NIAID director Anthony Fauci, said in a statement. " Better ways to diagnose, treat and prevent E. coli O157:H7 infections are badly needed. This new information will provide important leads to scientists working to reduce the human and economic burdens of this important pathogen."

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