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Wong, Catherine Wai Yee

University of British Columbia

Salmonella enterica (S. enterica) is a leading bacterial pathogen for foodborne outbreaks in fresh produce. The industry uses chemical washes or sanitizers to reduce pathogens, but natural foods without chemical intervention have been gaining popularity. This has led to rising interests in using bacteriophages, a virus that targets bacteria. To determine the efficacy of bacteriophages against S. enterica on post-harvest produce, the efficacy of a bacteriophage cocktail against S. enterica strains on Romaine lettuce leaf and cantaloupe flesh was examined for objective 1. Populations of S. enterica were reduced by 1–4 log CFU/cm². However, populations of S. Thompson were not significantly different (P > 0.05) from the controls after day 0. Thre was only one bacteriophage application for objective 1 and this led to determining if repeated bacteriophage applications could further reduce S. enterica populations on pre-harvest produce for objective 2. Bacteriophage cocktails were applied against S. enterica strains daily on germinating alfalfa sprout seeds from day 0–7. The results showed S. Enteritidis to be most susceptible to both cocktails. S. enterica populations on all strains continued to proliferate even with repeated daily bacteriophage applications, but populations were decreased compared to just one bacteriophage application. The population resurgence after repeated applications led to a third objective to determine if there is an optimum bacteriophage MOI and how S. enterica behaves mechanistically after bacteriophage treatment. For objective 3, two bacteriophage cocktails were co-inoculated with S. enterica strains at different MOIs, and the expression of selected genes were examined. MOI 1000 was the most optimal and reduced S. Enteritidis populations to undetectable levels from day 0 – 3. Cas1, mod and hsdS genes were highly upregulated between 2.5 – 5-folds for S. Enteritidis S5-483 and S. Typhimurium S5-536. The results of this study showed that bacteriophages can reduce S. enterica populations and repeated bacteriophage applications can further reduce S. enterica populations on fresh produce. The understanding into the transcriptional response of S. enterica after the bacteriophage treatment gives further insight into how S. enterica can survive bacteriophage treatment and ways to target S. enterica more effectively.

Text

2025-01-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86979

Food Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/