Madison -- The newly completed genomic sequence of E. coli O157:H7 reveals how these potentially deadly bacteria are armed with a surprisingly wide range of genes that may trigger illness.
A team of more than two dozen scientists from the University of Wisconsin-Madison Genome Center announced the completed genome in the upcoming Jan. 25 issue of the journal Nature.
The group discovered "islands of pathogenicity" across the genome that were picked up in entire clusters, possibly from other bacteria through the use of viruses. This ability for large-scale genetic change may make it harder to control the public health threat.
This strain of E. coli O157:H7 causes an estimated 75,000 illnesses a year in the United States, including numerous deaths, and is especially dangerous to vulnerable populations such as children, the elderly and people with challenged immune systems. The food-borne pathogen was first identified in 1982 from an outbreak from contaminated hamburger, and reported cases have risen steadily.
After completing the sequence of the O157:H7 strain, the researchers were able to compare that genome with E. coli K-12, a benign strain of bacteria sequenced in 1996 by Genome Center Director Fred Blattner. The team expected to find a few hot zones on which to concentrate, but instead found differences across the genome.
"The sheer magnitude of the differences was totally shocking to us," says lead author Nicole Perna, an assistant professor of animal health and biomedical sciences. "We couldn't just zoom in on areas of difference between the two species. The changes were scattered throughout."
The two strains of E. coli share about 3,500 common genes. But the O157:H7 strain had 1,300 additional genes that were not found in the harmless strain. The benign "cousin" bacteria also had 530 unique genes that were not shared with O157:H7.