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Carst and Walker
E coli plates

Ecoli hunting: new rapid detection methods used

Strain-specific tests have quickly ruled out bean sprouts as the cause of the deadly E coli outbreak in Germany. German bean sprouts were declared dangerous on Monday morning and safe by Monday afternoon.

Bean sprouts were briefly added to the list of foods seen as potential sources of E. coli 0104 — a new strain that has infected more than 2 300 people and killed 24 in Germany over the past three weeks. The list of potentially dangerous foods includes cucumbers, lettuce, tomatoes, and other raw salad vegetables.

The rapid reprieve for sprouts can be attributed to the availability of high-speed pathogen-specific tests. These assays, laboratory procedures that measure the biochemical activities of food samples, can now return reliable results in as little as 10 to 24 hours.

“As soon as we finished sequencing the DNA of this strain, we made the results public, like any ethical company would,” says Nir Nimrodi, head of food safety at Life Technologies, which has developed a custom test for E. coli 0104.

Life Technologies, a California-based biotechnology company with laboratories in Darmstadt, Germany, started shipping custom testing kits to European laboratories this week so that food suspected of carrying the pathogen could be tested as quickly as possible.

“We all have E. coli right now in our bellies,” Nimrodi says, “but not all the strains are dangerous, and even fewer of them are deadly to those infected. And if you use a general E. coli test, even if it tests positive, it does not mean you have discovered a source. With a strain-specific test, you can find out if you have been watering plants with infected water and need to stop, or if you have a specific crop of vegetables that are affected and need to be recalled.”

It can take as long as 10 days to gather results using traditional laboratory testing methods, but the new test can determine the presence or absence of the hybrid E. coli pathogen in hours.

“It has implications for public health and epidemic monitoring,” says Michael Somers of Children’s Hospital Boston. “The less time you have to spend growing patient specimens and subtyping something like E. coli, the easier it is to find the source of an epidemic.”

He added that “about 10 percent of the people infected with E. coli develop hemolytic uremic syndrome (HUS).” The kidney infection develops four to 10 days after bloody diarrhea appears. Some 90 percent of HUS cases in children are attributed to E. coli infections.

According to researchers, the new strain is a hybrid of enteroaggregative E. coli (EAEC) and enterohemorrhagic E. coli (EHEC).

EAEC was first identified in 1987 and is well-documented as a cause of persistent diarrhea, especially in children in the developing world, and as a food pathogen that is increasingly resistant to antibiotics in industrialized countries. EHEC is associated with hemorrhagic colitis and HUS. It is the leading cause of acute renal failure in children.

Source: MIT Technology Review

Addendum: 10 June 2011

Investigators have determined that German-grown vegetable sprouts are the cause of the E. coli outbreak that has killed 29 people and sickened nearly 3 000, the head of Germany’s national disease control center said Friday, June 10, 2011. Reinhard Burger, president of the Robert Koch Institute, said even though no tests of the sprouts from an organic farm in Lower Saxony had come back positive for the E. coli strain behind the outbreak, an investigation into the pattern of the outbreak had produced enough evidence to draw the conclusion.

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