Genes of dangerous E. coli mapped

Scientists have mapped the genetic blueprint of a form of bacteria which causes severe food poisoning and sometimes death.

Dr Nicole Perna and a team from the University of Wisconsin in Madison have sequenced the 5,000 genes of Escherichia coli 0157:H7. It is a particularly dangerous form of the common E. coli bacteria which has caused death after food poisoning both here and abroad.

E. coli arises in food through faecal contamination and is often found in ground beef. It is readily destroyed with thorough cooking but under-cooking or improper handling of foods can allow it to persist.

A large outbreak of E. coli 0157:H7 occurred in Japan involving 6,000 schoolchildren. They were infected through uncooked radish sprouts. Those most at risk are the elderly and the young.

The illness brought on by 0157:H7 causes a severe form of bloody diarrhoea and sometimes kidney failure and death. Most E. coli bacteria cause much less severe symptoms.

The new 0157:H7 gene map was compared to the list of genes in ordinary E. coli and 1,300 new genes were discovered, the authors write in the journal, Nature. The comparison is highly valuable because it helps scientists to find the specific differences which make 0157:H7 so dangerous.

"We've identified an enormous number of new genes that may or may not be involved with the pathogenesis and the survival of this organism in the gut," Dr Perna said.

She expects the gene sequence will spark follow-up research to identify the virulent factors as well as new genetic markers to help detect E. coli more easily in people or contaminated food.

One of the team's most interesting findings is that 0157:H7 might have picked up its new genes from other bacteria. These could have been transferred through bacterial viruses which invade bacteria in the same way they invade humans. The viruses would have been carriers of these extra genes which were then inserted in less dangerous E. coli forms.

--(Additional reporting, Reuters)