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UBC Theses and Dissertations

Isolation of Listeria species and characterization of Listeria monocytogenes from a ready-to-eat seafood processing facility in British Columbia : examination of source, persistence, and risk Johnston, Keely Nicole


Foodborne Listeria monocytogenes (Lm) causes listeriosis, a rare but severe disease affecting at risk populations. Contamination of ready-to-eat (RTE) food has been linked with persistent Lm in the food processing environment (FPE), though mechanisms of persistence are not fully understood. Recent surveys in British Columbia (BC) detected Lm in seafood processing facilities and in RTE seafood products, yet little is known regarding Lm persistence and risk posed by strains from these sources. The objectives of this study were to determine the prevalence of Listeria spp., including Lm, in a RTE seafood processing facility and assess persistence capabilities and potential risk of Lm recovered. Environmental and RTE food samples were collected over 18 months from a BC seafood processor (n=2,959) and assessed for the presence of Listeria spp. Isolated Lm were subjected to phenotypic and genetic characterization and a subset of isolates (n=28) were characterized for attributes that may facilitate FPE persistence: surface adherence, resistance to quaternary ammonium-based sanitizers, and adaptation to salt and refrigerated temperatures. Ability of cold-smoked salmon from this processor to support Lm growth, evaluation of virulence gene (inlA) sequence, and antibiotic resistance in the subset were used to assess consumer risk. Non-Lm Listeria spp. and Lm were found in 2.6% and 1.5% of samples, respectively. Molecular characterization revealed raw materials as the primary contamination source and two recurrent subtypes. Lm typically possessed one attribute favorable to persistence in the FPE, though there was no association between these attributes and strain recurrence. Cold-smoked salmon supported the growth of Lm and most strains recovered in the FPE (n=14) belonged to serotypes linked to listeriosis (92%) and possessed full-length inlA (93%). These strains, however, did not show resistance to antibiotics commonly used to treat listeriosis. The results of this study highlight the importance of processor-level control strategies to minimize Lm FPE persistence, product contamination, and risk to consumers. While these results improve understanding of Lm in a BC seafood processing environment, more work is needed to determine whether these strains are truly persisting in this FPE and how these findings compare to similar facilities.

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