A confocal scanning laser micrograph of fluorescent green E. coli gaining access to the xylem of cut leaf lettuce.  Click the image for additional information about it.

New, Quicker Tests Identify E. Coli Strains

New tests that more quickly identify dangerous strains of Escherichia coli bacteria are being developed by Agricultural Research Service scientists in Wyndmoor, Pa.

ARS microbiologist Pina M. Fratamico, at the agency's Eastern Regional Research Center (ERRC) in Wyndmoor, is working with Pennsylvania State University to develop tests that quickly identify E. coli strains.

Certain E. coli strains, such as O157:H7, causes serious diseases, including bloody diarrhea and hemorrhagic colitis. Infections may result in serious health complications, including kidney failure. Other E. coli serogroups, including E. coli O26, O111 and O121, also cause gastrointestinal illnesses in humans.

Currently, scientists commonly use a procedure called serotyping to distinguish between different types of E. coli--some harmful, others harmless. However, this procedure is time-consuming and labor-intensive.

Fratamico, with ERRC's Microbial Food Safety Research Unit, and her team are developing both conventional and real-time polymerase chain reaction (PCR) tests. These chemical procedures generate enough of a bacterium's genetic material so that it can be studied and identified. With one real-time PCR reaction, four products can be amplified simultaneously and detected in "real time" as they multiply.

Scientists have little information about some individual E. coli serogroups; therefore, the number of diseases these organisms cause is likely underestimated. Fratamico is targeting genes in the E. coli O-antigen gene clusters so researchers can detect and identify specific serogroups and increase knowledge about each one's potency.

In one study, a real-time PCR assay was more sensitive than other detection methods. According to Fratamico, the U.S. Department of Agriculture's Food Safety and Inspection Service has expressed interest in the new PCR tests for detection and confirmation of not only E. coli O157:H7, but of other E. coli strains as well.

ARS is the USDA's chief scientific research agency.