Efficacy of Listeria Phage in Reducing Listeria monocytogenes under Both Experimental and Food Processing Conditions
Listeria monocytogenes (L. monocytogenes) is a foodborne pathogen able to flourish in different food processing environments. Bacteriophages are viruses that target bacteria and may be effective in controlling bacterial contamination in different environments. In 2006, the US Food and Drug Administration approved a six-Listeria phage product for use as a food additive in controlling Listeria contamination in ready-to-eat meat and poultry products. In this study, we evaluated the efficacy of bacteriophages in controlling Listeria monocytogenes growth on non-food contact surfaces under different conditions. Stainless steel coupons or sterilized bags were inoculated with Listeria monocytogenes (LM94 or LM-GFP) and a cocktail of six Listeria bacteriophages under conditions that could limit or enhance phage treatment efficacy: pre-treatment of coupons with phages, protection of phages in oil, presence of competing organic matter, and presence of competing bacteria. In each case, inoculated coupons or bags were incubated for 18 h at 21°C and Listeria monocytogenes concentrations were compared between phage-treated and untreated samples. Phage impact on L. monocytogenes growth was measured by ANOVA through comparing viable bacteria cell counts between phage treated and untreated group with two sample t-tests and WMW tests based on data distributions. Differences were considered statistically significant at P < 0.05. Phage treatment significantly reduced Listeria monocytogenes on stainless steel coupons co-inoculated with bacteria and bacteriophages (P < 0.05). Phage treatment remained effective in the presence of soil, fat, and competing (non-Listeria) bacteria (P < 0.05). Phage treatment was not effective, however, in reducing bacterial concentrations in the presence of blood, as well as when used as a preventative, i.e., phages applied to coupons 4 h prior to Listeria challenge. Protecting phages in oil prior to application did not significantly improve efficacy of the treatment. These data indicate that Listeria phages may be effective in reducing Listeria monocytogenes contamination of non-food contact surfaces in food processing environments. Under some conditions, however, phages may need some form of protection to ensure their efficacy (e.g., to prevent desiccation and inactivation).
Ebner, Purdue University.
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