E. Coli Genetic Code Deciphered

Scientists have decoded the DNA of a lethal strain of E. coli bacteria â€” an advance that could one day save lives and prevent thousands of illnesses each year. <br><br>The complete genetic blueprint

Wednesday, January 24th 2001, 12:00 am

By: News On 6

Scientists have decoded the DNA of a lethal strain of E. coli bacteria â€” an advance that could one day save lives and prevent thousands of illnesses each year.

The complete genetic blueprint of E. coli type O157:H7 should help guide scientists toward the creation of a vaccine against the germ for cattle and other animals. That, in turn, would lower the risk that people will get sick from contaminated hamburger or other sources.

``Now we have the whole picture,'' said James Kaper, a University of Maryland microbiologist who specializes in E. coli research.

At the same time, the decoding shows that finding a vaccine won't be easy: The researchers discovered that the E. coli strain frequently picks up swatches of genetic material from other bacteria and viruses. That might explain why it is so potent and hard to treat.

The study was done by a team of more than two dozen University of Wisconsin researchers and others.

While harmless E. coli lives in the gut of humans, the dangerous type has been responsible for major outbreaks of disease since 1982, when it was first identified in contaminated hamburger. It causes a severe form of bloody diarrhea and can cause serious, even fatal, kidney damage.

About 73,000 people were infected last year in the United States, and 60 died, according to the federal government. The infections are most dangerous to young children and the elderly.

In 1993, an E. coli outbreak in the Seattle area nearly sank the Jack in the Box fast food chain. More than 600 people fell ill and four died after eating contaminated hamburger.

Food such as hamburger should be cooked thoroughly because the bacteria are resistant to heat.

The new work is reported in Thursday's issue of the journal Nature by Fred Blattner and Nicole Perna at Wisconsin, who had already mapped a harmless version of E. coli. They were surprised to find that the DNA makeup, or sequence, of the dangerous strain was so different.

``The perception when we started was, `Why do we need to sequence another E. coli? How different can they be?''' Perna said. ``And I think this genome has shown why it was so important. The differences are scattered throughout the whole chromosome. This genome has been pieced together by a lot of different events over evolutionary time.''

Scientists found that the virulent strain of E. coli shares about 3,500 genes with its harmless cousin. But the E. coli O157:H7 strain has about 1,300 additional genes, while the harmless strain has 530 genes not found in O157:H7.

``The sheer magnitude of the differences was totally shocking to us,'' Perna said.

Some of the genes the virulent strain has imported from other bacteria and viruses may make the germ hard to treat and fight with a vaccine, Perna said.

The two strains of E. coli bacteria probably began to diverge about 4.5 million years ago, the researchers said, a relatively short time on the evolutionary scale of hundreds of millions of years.

The emergence of E. coli O157:H7 in just the past 20 years suggests even a slight change can have a serious impact, researchers said.

``Bacteria have a big advantage because they can come up with mutations and variations faster than we can stop them,'' Kaper said.