Efficacy of Commercial Phage Based Treatment as a Control Strategy against Listeria Spp. and Effect of Host Characteristics on Lytic Capacity
Listeria monocytogenes can persist on food contact (FCS) and non-food contact surfaces (NFCS) and enter the food continuum by cross-contamination. Meat processing facilities are a known source of Listeria spp. contamination. Specificity and safety of use render bacteriophages suitable to control Listeria spp. in foods and food environments. Previous research has shown that host characteristics can affect lytic efficacy of bacteriophages. This study focuses on evaluating how phenotypic and genotypic characteristics of Listeria hosts influence lytic capacity of a commercial listeriophage cocktail in vitro. We also investigated the efficacy of listeriophage as a biocontrol strategy for Listeria spp. on non-food contact surfaces (NFCS) in a meat processing facility. In vitro lytic capacity was tested quantitatively using spot assay for 475 Listeria spp. isolates with varied phenotypic (attachment capacity, sanitizer tolerance) and genotypic (PFGE) characteristics. Lytic capacity was measured quantitatively for 55 isolates by monitoring growth of L. monocytogenes cultures with and without listeriophage over time and enumerating bacterial counts after 4h. Fifty-nine NFCS were tested in a meat processing facility for Listeria spp. weekly for three weeks. Each Listeria spp. positive site was treated with commercial phage then assessed for reduction in Listeria spp. Although enhanced attachment capacity and sanitizer tolerance of Listeria spp. isolates did not significantly (p>0.05) influence phage susceptibility in vitro; history of persistence, incubation temperature, and concentration of listeriophage treatment were critical. Quantitatively, listeriophage treatment significantly (p<0.001) affected growth and reduced bacterial counts of Listeria spp. compared to control samples. A total of 15, 21, and 14 sites were positive for Listeria spp. at weeks one, two, and three, respectively. Post-treatment Listeria spp. were detected in 12/23 sites, and numerically reduced in 4/12 sites by an average of 2.1 log CFU/sponge. Among the isolates subjected to spot assay, 60% strains showed low susceptibility to listeriophage, 36% showed moderate lysis, and 4% isolates showed confluent lysis by listeriophage. This study illustrates influence of bacterial host characteristics on lytic efficacy of listeriophage treatment. Further, we have preliminary evidence for listeriophage as a potential control strategy in food environments.
Oliver, Purdue University.
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