Bacteriophage Mixture Inactivation Kinetics against Escherichia Coli O157:H7 on Hard Surfaces

Abstract

AbstractThis study determined the effect of previously described phage cocktail (BEC8) on the inactivation kinetics of a mixture of Escherichia coli (EHEC) O157:H7 strains on food processing surface materials: stainless steel chip (SSC), ceramic tile chip (CTC) and high‐density polyethylene chip (HDPEC). EHEC strains were combined and spot‐inoculated on surfaces in dried or liquid form and BEC8 was applied and incubated at 12, 23, 30 and 37C. EHEC survival was determined on tryptic soy agar. D values ranged from 3.9 min at 37C to 46.7 min at 12C. Z values calculated for SSC, CTC and HDEPC resulted in 26.1, 23.7 and 26.7C for dry cells, respectively, and 23.2, 23.7 and 24.5C for liquid cells, respectively. There was a significant difference in the rate of bacterial inactivation between lower (12 and 23C) and higher temperatures (30 and 37C). These results indicated that BEC8 killed EHEC on hard surfaces rapidly following first‐order kinetics.Practical ApplicationsThe effect of a previously described phage cocktail (BEC8) on the inactivation kinetics of a mixture of Escherichia coli (EHEC) O157:H7 strains applied on hard food processing surface materials was studied. The results indicated that phages killed EHEC on hard surfaces relatively rapidly following a predictable rate. However, one must consider the long times to achieve a 5‐log reduction when initial cell counts are high. It would take approximately 2–4 h for a 5‐log cfu reduction of liquid cells at 23C. Both the time length and the temperature of application must fit within the industry time scales.