P1-38 Gaseous Ozone and Bacteriophage Act Synergistically against Escherichia coli O157:H7 on Spinach Leaves

Monday, August 1, 2016
America's Center - St. Louis
Mustafa Yesil, The Ohio State University, Columbus, OH
David Kasler, The Ohio State University, Columbus, OH
En Huang, The Ohio State University, Columbus, OH
Ahmed Yousef, The Ohio State University, Columbus, OH
Introduction: Contamination of fresh produce with enterohemorrhagic Escherichia coli (EHEC) remains one of the leading causes of foodborne disease outbreaks in the United States. Low infective dose of EHEC and minimal post-harvest processing of fresh produce necessitate the search for effective disinfection approaches to protect the public against disease outbreaks and the produce industry from economic losses.

Purpose: In this study, we investigated the efficacy of gaseous ozone during vacuum cooling and subsequent application of bacteriophage for inactivation of E. coli O157:H7 on fresh produce.

Methods: Spinach leaves were spot-inoculated with low or high concentrations of E. coli O157:H7 (5.3 or 6.6 log CFU/g, respectively). Inoculated leaves were subjected to gaseous ozone during vacuum cooling as follows: initially 28.5 in. Hg vacuum was applied, followed by gaseous ozone treatment at 1.5 g ozone/kg ozone-oxygen gas mix, at 10 psig vessel pressure, and 30 min holding time. Ozone-treated leaves were sprayed with E. coli phage at 8.3 log PFU/g, then held for five minutes.

Results: At 5.3 log CFU/g inoculum level, gaseous ozone alone significantly (P < 0.05) reduced E. coli population by 3.1 log CFU/g when compared to inoculated untreated control. Sequential treatment of ozone and bacteriophage significantly (P < 0.05) reduced E. coli populations below the detection limit of the enumeration method (i.e., < 1 log CFU/g). At 6.6 log CFU/g, gaseous ozone and sequential treatments significantly (P < 0.05) reduced E. coli counts by 1.8 and 5.2 log CFU/g, respectively. 

Significance: Regardless of inoculum size, sequential treatments considerably decreased the risk of contamination of fresh produce with E. coli O157:H7. Considering the realistic low contamination levels of fresh produce and low infective dose of E. coli, sequential application of gaseous ozone and bacteriophage seems a promising post-harvest disinfection method to secure the safety of produce.