Targeting E. Coli’s Lesser-Known Siblings

The U.S. Department of Agriculture (USDA) is working to develop user-friendly test kits for six lesser-known siblings of Escherichia coli O157:H7, the bacterium that has caused a number of major foodborne illness outbreaks in the U.S. over the past 30 years.

They’re a heterogeneous group of organisms, but they all can cause serious illness.

Pina Fratamico, PhD, U.S. Department of Agriculture

“Once O157 started causing illness in the early 1980s, investigators developed methods to detect that pathogen,” said Pina Fratamico, PhD, research leader of the Molecular Characterization of Foodborne Pathogens Research Unit at the U.S. Department of Agriculture (USDA).

But the “Big Six” serogroups of O157 relatives, O26, O45, O103, O111, O121, and O145, have gotten less attention and have also proven harder to characterize.

“They’re a heterogeneous group of organisms, but they all can cause serious illness. We don’t have a clear handle on what the unique set of genes is that makes that so,” Dr. Fratamico said. “Are there clones that are spreading? There are mobile genes among E. coli strains that move from organism to organism, and possibly some strains are acquiring key virulence genes that are important for pathogenesis.”

Two genes that are frequently found in the E. coli strains that cause more serious illness are the eae and shiga toxin genes, Dr. Fratamico said.

There are a number of key elements necessary for developing good detection methods for these serogroups, Dr. Fratamico said, including a good selective differential plating medium, an enrichment medium, and tools such as latex reagents. While there are some commercial detection kits available from Europe, those do not target the O121 and O145 strains, both of which have been implicated in significant U.S. outbreaks. For example, O145 was the culprit in 2010, when lettuce contamination sickened at least 29 people in Michigan, Ohio, and New York.

“Our research is focused on keying in on the characteristics of these organisms that make them pathogenic and the biomarkers in food we should be looking for,” Dr. Fratamico said. “What’s more, although these top six have been identified, we need to be on the watch for other pathogenic clones that might emerge, because genes are easily shared among E. coli.”

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