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

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.