Comparison of the difco EZ coli(TM) rapid detection system and Petrifilm(TM) test kit-hec for detection of Escherichia coli O157:H7 in fresh and frozen ground beef

The Difco EZ Coli(TM) Rapid Detection System was compared to the 3M Petrifilm(TM) method for detection of Escherichia coil O157:H7 in raw ground beef. Raw meatballs (25 g) were inoculated with 10 to 15 cells of Escherichia coli O157:H7, stored for various times and at different temperatures, and then stomached for 2 min in 225 ml of EZ Coli(TM) enrichment broth, which was then incubated at 42°C for 18 to 24 h. A 1-ml sample of the enrichment broth was loaded into the top of the detector tips and the remaining EZ Coli(TM) broth held at 35°C before streaking onto MacConkey sorbitol agar and tryptic soy agar with yeast extract. A duplicate set of meatballs were tested using the 3M Petrifilm(TM) Test Kit-HEC for hemorrhagic Escherichia coli O157:H7. In this method raw meatballs (25 g) were enriched for 6 h in modified EC broth containing novobiocin at 37°C prior to inoculation of the Petrifilm(TM) E. coli Count Plates, which were incubated at 42°C for 18 h. The immunoblot ELISA was performed following this incubation. Presumptive positive isolates from both methods were confirmed using Oxoid E. coli Latex Agglutination and Difco Pasco ID Tripanels. Both methods permitted detection of 10 to 15 cells of E. coli O157:H7 per ml (i) immediately following inoculation, (ii) after 3 days of refrigerated storage at 8°C, and (iii) after 30 days in frozen storage at -20°C. The Difco EZ Coli(TM) Detection System proved to be a simpler and faster screening method with identification of negative and presumptive positive samples within 15 to 18 h.