More Accurate E. coli Screening Tests to Ensure Food Safety and Reduce Food Waste

Background

Shiga-toxin producing Escherichia coli (STEC) are the main food safety concern in Canadian beef. The food safety interventions that have been developed and implemented at beef processing facilities have been designed to combat STEC, and rapid screening tests have been developed to detect whether STEC have evaded those food safety interventions and found their way into Canadian beef. When the screening test indicates that STEC may be present (i.e., a “positive” test result), the beef needs to be held for confirmatory testing. This can take several days, so sometimes the beef is simply discarded.

For example, one of the best-known STECs is E. coli O157:H7. Current screening tests look for the genes responsible for the “O” part, but whether it carries the stx and eae virulence factors that make it dangerous to people. As a result, rapid screening tests may produce “false positives”, meaning that even though E. coli O157 were present, they may not be pathogenic. When this happens, safe beef has been wasted. This is obviously very costly. On the other hand, if a high percentage of E. coli O157:H7 are virulent, then confirmation tests will not be necessary.

Objectives

• Determine the likelihood of false positives by the current E. coli O157:H7 testing methods

What they will do

This team will collect microbiological samples from two federally inspected beef processing facilities. The E. coli in the samples will be enriched and analyzed to detect which STEC serotypes and virulence factors are present. The O157-positive samples will be cultured, and individual E. coli O157 strains will be isolated and sequenced to see if they are carrying virulence factors.

Implications

This project will assess how common “atypical” E. coli O157 are, and work to develop more sensitive screening tests that will selectively detect pathogenic STEC. This will ensure food safety for consumers while reducing unnecessary food waste.