A Purdue University research team has developed a new time-saving assay to detect Escherichia coli O157:H7 in ground beef. Development of the assay was led by Bruce Applegate, Ph.D., Professor of Food Science at Purdue.
The U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA’s FSIS) has a “zero tolerance” policy for E. coli O157:H7, meaning that if a single cell is detected in a standard 325-gram or 11.4-ounce sample of ground beef, the entire batch is flagged as unfit for consumption. However, detecting pathogens at such low concentrations requires enrichment.
The new assay developed by Dr. Applegate and his team saves time, as it is designed so that sample enrichment and pathogen detection both occur during the 15 hours or more needed to ship samples from a production facility to an FSIS testing laboratory. This enables product to be released onto the market more quickly, as the assay will provide a positive or negative result by the time the product is received by FSIS.
The technology is based on phages, which are viruses that infect specific bacteria. Researchers genetically modified a phage so that, after infecting E. coli O157:H7, it would integrate its genome into the bacterial cells’ chromosome. Once integrated into the E. coli chromosome, the phage produces an enzyme that makes light and causes the infected cells to glow. A glowing culture indicates the presence of E. coli O157:H7.
Two co-authors of the study are Arun Bhunia, Ph.D., a Purdue Professor of Food Science, and Andrew Gehring, Ph.D. and George Paoli, Ph.D. of USDA’s Agricultural Research Service (ARS) in Wyndmoor, Pennsylvania. Dr. Gehring and Dr. Paoli’s collaborations with Dr. Applegate are part of a longstanding cooperative agreement between ARS and Purdue’s Center for Food Safety Engineering.