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USDA explores faster E.coli detection method

By Joe Whitworth , 02-Jan-2013

A new real-time polymerase chain reaction (PCR) system offers a “promising method” for testing for shiga toxin-producing E.coli (STEC) in food samples, according to the US Department of Agriculture (USDA).

Researchers found that the GeneDisc assays for STEC detection are rapid, simple and accurate and can be used for screening pathogens in ground beef and could be used on other foods.

They added that the availability of rapid screening methods for STEC is critical.

The test detects the presence of specific gene targets that indicate the existence of STEC in meat.

New PCR systems

PCR protocol has been used in the meat industry but the new generation of real-time PCR systems, like the GeneDisc from Pall Technologies in France, employ a self-contained unit that standardizes the procedure and can be portable and easy to use – offering advantages for meat processors and inspectors from industry and government.

The aim of the study was to compare two different enrichment types and evaluate GeneDisc real-time PCR assays to detect nine STEC serogroups: STEC O26, O45, O91, O103, O111, O113, O121, O145, and O157 in ground beef.

Pina Fratamico, researcher at the USDA Agricultural Research Service in Wyndmoor, Pennsylvania, said a method that has flexibility, is sensitive and less time consuming would be more amenable for use by regulatory agencies and industry.

"Testing using these types of systems is faster, easier, and more reproducible than previous methods, and this should increase food safety in the long run,” said Fratamico.

“I feel that we could confidently move to these new systems for screening ground beef and other foods for E.coli contamination.”

Simultaneous detection

The technology allows simultaneous detection of multiple targets by real-time PCR, wrote the researchers in Frontiers in Cellular and Infection Microbiology.

GeneDisc real-time PCR assays were evaluated for detection of the stx1,stx2eae, and ehxA genes and a gene that identifies the O157 serogroup followed by a second assay targeting serogroup-specific genes of STEC O26, O45, O91, O103, O111, O113, O121, O145, and O157. 

“The assays were specific for the target organisms, and the sensitivity was <10 bacteria/sector. However, the stx1/stx2 assay required >100 bacteria for a positive result. Strains carrying the stx2f variant and the eae rho variant were not detected,” said the researchers.

USDA’s Food Safety and Inspection Service (FSIS) declared the top six non-O157 STEC as adulterants in raw, non-intact beef products and began testing for the STEC serogroups in June 2012.

"Certain groups of STEC have been declared as adulterants by the USDA FSIS, and the availability of rapid and reliable tests for these pathogens is critical so that testing results are available before meat is shipped to restaurants and consumers,”  added Fratamico.

Source: Frontiers in Cellular and Infection Microbiology

Published online ahead of print: doi: 10.3389/fcimb.2012.00152

“Detection of Shiga Toxin-Producing Escherichia coli in Ground Beef Using the GeneDisc Real-Time PCR System” 

Authors: Fratamico Pina, Bagi Lori K.

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