Purpose: To assess the feasibility of PhageDx E. coli O157:H7 Assay to detect fewer than three CFU E. coli O157:H7 in 100 ml water in 4 h, from sample preparation to results.
Methods: Water samples (100 ml) were inoculated with known numbers of E. coli O157:H7, filtered onto PVDF membranes, enriched for 2 h, and infected with a luciferase-expressing recombinant E. coli O157:H7 phage for 2 h. Enrichment and infection steps were performed directly on the filter membrane. One-hundred microliters of samples were transferred to a 96-well plate, substrate was added, and signals were measured in a standard luminometer.
Results: A single CFU of E. coli O157:H7 was detected in 100 ml room-temperature water samples in 4 h with signals ranging from 3- to 6-fold above background. Host-range studies of the E. coli O157:H7 phage indicates it is highly specific for E. coli O157:H7 as positive luciferase signal are seen with 58 E. coli O157:H7 strains, while little or no signal was observed with 132 other bacterial strains, including commensal E. coli, 12 non-O157:H7 Big 6 STEC, and other coliforms.
Significance: Current water testing methods are characterized by 12 - 24 h time-to-results, visual identification of samples, and the possibility of missing potentially contaminated samples. The option to test water samples quickly and accurately would benefit irrigation and drinking water testers, as well as beverage and vegetable producers.