Impact of Nisin on Proliferation of Background Microbiota, Pressure-Stressed and Wild-Type Listeria monocytogenes, and Listeria innocua During a Real-Time Shelf-Life Study

With the rapid implementation of high-pressure processing in many sectors of the food industry, considerations associated with pressure-stressed microorganisms are emerging. Nisin was utilized in this study for controlling the proliferation of <i>Listeria monocytogenes</i> and <i>L. innocua</i> inoculated on cold-smoked trout during a 4-week refrigerated shelf-life trial. Wild-type and pressure-stressed phenotypes of <i>Listeria</i> were compared in this study. The pressure-stressed phenotypes were prepared by treating the surrogate strain and pathogen mixture at 103.4 MPa (15K PSI) for 20 min. <i>L. monocytogenes</i> multiplied extensively during the 4-week refrigerated trial and counts were increased (<i>p</i> < 0.05) from 3.68 ± 0.1 log CFU/g on the first week to 6.03 ± 0.1 log CFU/g. Both phenotypes and the surrogate microorganisms illustrated similar (<i>p</i> ≥ 0.05) multiplication trends. Unlike samples subjected to water treatment, nisin was effective (<i>p</i> < 0.05) in keeping the microbial counts lower compared with the controls, particularly earlier during the shelf-life trial. Our study illustrates that the selected surrogate microorganism has comparable sensitivity to nisin relative to <i>L. monocytogenes</i> and thus could be used interchangeably in future public health microbiology challenge studies with similar scope. Additionally, we observed that pressure-stressed <i>L. monocytogenes</i> has proliferation and sensitivity to nisin comparable to wild-type pathogen.