P2-51 A Novel Phage-based Escherichia coli O157:H7 Detection Method for Ground Beef

Tuesday, August 2, 2016
America's Center - St. Louis
Steve Erickson, LabCorp, New Brighton, MN
Jose Gil, LabCorp, Los Angeles, CA
Ben Hopkins, LabCorp, Los Angeles, CA
Minh Nguyen, LabCorp, New Brighton, MN
Dwight Anderson, LabCorp, New Brighton, MN
Introduction: Existing protocols for detection of E. coli O157:H7 in foods are complicated, expensive, slow, labor-intensive and prone to false positives. The PhageDx E. coliO157:H7 Assay was developed to address most of these shortcomings, offering beef producers an effective, fast and simple testing alternative.

Purpose: To assess the feasibility of PhageDx E. coli O157:H7 Assay to detect at least one CFU of E. coli O157:H7 in 25 g ground beef (GB) in less than 7 h, from sample preparation to results.

Methods: GB samples (25 g) were inoculated with E. coli O157:H7 and stored for 24 h. GB was mixed at 1:3 with tryptic soy broth, homogenized, incubated for 5 h, centrifuged (10 ml aliquot), and infected with a luciferase-expressing recombinant E. coli O157:H7 phage for 2 h. After substrate addition, samples were read directly in a luminometer.

Results: A single CFU of E. coli O157:H7 was detected in GB samples after 7 h in 21 separate samples. All 58 E. coli O157:H7 strains yielded a strong positive signal when tested in pure culture. None of 132 other bacteria, including 12 non-O157:H7 STEC strains, 120 commensal E. coli, and other coliform, Listeria, Salmonella, and Staphylococcus species, yielded positive luminometer signals when tested in pure culture. 

Significance: The PhageDx E. coli O157:H7 Assay offers a valuable testing alternative for beef producers compared to the most commonly used protocols. Benefits include a time-to-results (TTR) reduction of approximately 40% to 50% to release inventory faster, a simple five-step protocol, and fewer false positives.