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
New, Quicker Tests Identify E. Coli
Strains By Jim
December 31, 2003
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.