Direct Enumeration of Escherichia coli O157:H7 from Petrifilm™ EC Count Plates Using the Petrifilm™ Test Kit — HEC Without Sample Pre-Enrichment

Abstract

Enumeration of Escherichia coli O157:H7 from Petrifilm™ E. coli (PEC) Count plates was studied incorporating the Petrifilm™ -HEC kit without sample pre-enrichment. Samples containing various E. coli O157:H7 inoculum levels were plated according to PEC package insert instructions. Plates were incubated at 32°C for dairy products and at 35°C for other samples. Total coliform, E. coli and E. coli O157:H7 levels were quantified in both control and inoculated samples. The average recovery from various food matrices was 74.8%. Food samples included retail soft cheese, clams, ground beef, chicken, salad mix, apple juice, cantaloupe and raw milk. The overall recovery was also determined on surface samples including cutting boards and preparation tables, at 116.3%. Results suggest that enumeration of E. coli O157:H7 from PEC Count plates is possible for products containing background coliforms as high as 40,000 colony forming units (CFU)/g, and with minimal background coliforms at <10 CFU/g. This method is a fast and efficient means of quantifying levels of presumptive positive E. coli O157:H7 from PEC Count plates.