WI (24 Jan '01)- Enterohaemorrhagic Escherichia
coli (EHEC) O157:H7 is the full name of the toxic bacteria behind several
highly publicized outbreaks of food contamination in North America in recent
years. With the genome sequence of that killer bug now described, researchers
expect to learn much more about the pathogenesis and prevention of this food-bourne
In 1997, University of Wisconsin researchers published the sequence of a
common non-pathogenic form of E.coli found in lower intestine, the
K-12 strain. Since that time they have been able to identify the DNA sequence
of far more dangerous 0157:H7 variety, and have identified surprising and
important differences between the two strains. This kind of comparative genomics
helps researchers to better understand some of the basic processes of infection.
Map of E.coli O157:H7. Click for printable version.
A comparison of the genome of 0157:H7 with the harmless variety showed
remarkable similarity in some of the genetic components of each, but marked
discrepancies as well. Indeed, the investigators found 1,387 new genes in
the infectious variety of the bug. These new genes are very similar to genes
associated with infectious activity in other microorganisms such as Salmonella
and Shigella. Of particular interest are genes found in O157:H7
that encode toxic proteins known to be involved in the earliest stages of
gastrointestinal infection. Moreover, the sequence data suggests that at least
some of the rogue genes may have come from viruses interacting with the bacterial
Insights gained from comparing the evolution of different species of E.
coli could lead to much need treatments for infection caused by O157:H7
and related toxic variants. On a larger scale, the research will help to elucidate
how an organism becomes infectious. O157:H7 infection, associated with
eating raw or undercooked beef, kills more than 60 people and sickens 70,000
more in the United States each year alone. Worldwide, infection rates number
in the tens of millions.
The researchers instantly made the complete O157:H7 sequence available
online. The raw data is available on Entrez Genome database and an annotated
sequence has submitted to the public genome data site, GenBank. Their research
appears in the January 25, 2001 issue of Nature.
|A Quick Look at E. coli O157:H7
|Known Routes of Infection
- Eating meat, especially undercooked ground beef
- Consumption of sprouts, lettuce, salami, unpasteurized milk and
- Swimming in or drinking sewage-contaminated water
- Exposure to diarrheal stools of infected persons
|Course of Infection
Symptoms include severe bloody diarrhea and abdominal cramps with
little or no fever. Most cases resolve in 5 to 10 days. Up to seven
percent of cases lead to more serious problems including hemolytic
uremic syndrome, kidney failure and death.