Evaluation of culture- and PCR-based detection methods for Escherichia coli O157:H7 in inoculated ground beef

This month’s Journal of Food Protection (Volume 68, Number 8, Page 1566-1574) reports that currently, several beef processors employ test-and-hold systems for increased quality control of ground beef.
In such programs, each lot of product must be tested and found negative for Escherichia coli O157:H7 prior to release of the product into commerce. Optimization of three testing attributes (detection time, specificity, and sensitivity) is critical to the success of such strategies.
Because ground beef is a highly perishable product, the testing methodology used must be as rapid as possible. The test also must have a low false-positive result rate so product is not needlessly discarded. False-negative results cannot be tolerated because they would allow contaminated product to be released and potentially cause disease.
In a study published in the Journal of Food Protection, two culture-based and three PCR-based methods for detecting E. coli O157:H7 in ground beef were compared for their abilities to meet the above criteria.
Ground beef samples were individually spiked with five genetically distinct strains of E. coli O157: H7 and then subjected to the various testing methodologies. There was no difference in the abilities of the PCR-based methods to detect E. coli O157:H7. The culture-based systems detected more positive samples than did the PCR-based systems, but the detection times were at least nine hours longer than those for the PCR-based methods.
Ground beef samples were also spiked with potentially cross-reactive strains. The PCR-based systems that employed an immunomagnetic separation step prior to detection produced fewer false-positive results.