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UBC Theses and Dissertations

Characterization of food chain-derived Listeria monocytogenes and the role of Listeria genomic island (LGI1) in virulence, survival, and tolerance to food-related stress Kovacevic, Jovana


The presence of Listeria spp. and L. monocytogenes (Lm) was investigated in provincially inspected food processing and retail facilities in British Columbia. Lm (n=56) was recovered in food processing environment (FPE) of dairy, meat and fish facilities, and in ready-to-eat fish products. The majority of Lm belonged to listeriosis causing serotypes 1/2a and 4b. Isolate fingerprinting revealed 14 sequence types, and 38 pulsotypes, with 66% of Lm possessing the full-length inlA, a causally linked virulence determinant. Unexpectedly, 4b serotypes more readily acquired point mutations leading to rifampicin resistance compared to other serotypes (p<0.05). Lm that adapted more quickly to cold (4°C) also more often encoded a full-length inlA. No resistance to antibiotics used in listeriosis treatment was observed; however, a large proportion of isolates possessed resistance or reduced susceptibility (RSC) to ciprofloxacin (CIP, 75%) and clindamycin (CLI, 98%). When eight isolates were experimentally adapted to high concentrations of CIP, minimum inhibitory concentrations (MICs) of benzalkonium chloride (BAC) increased (n=5), gentamicin MICs remained the same (n=6) or increased 2-fold (n=2), and led to RSC to linezolid (n=1) and resistance to CLI (n=8). Tolerance to quaternary ammonium (QAC) sanitizers, BAC and E-San, was also investigated in a clinical Lm strain (08-5578) that possessed a previously uncharacterized island, LGI1. High tolerance to acid, cold, high salt conditions, and QACs was seen. Deletion of LGI1 genes lmo1851, emrE, and sel1, with putative regulatory, efflux, and adhesion functions, respectively, did not affect the acid, cold and salt tolerance, or the adhesion and invasion of TC-7 and HeLa cells. The ΔemrE mutant had impaired growth at sub-lethal concentrations of QACs, and up to three times lower MICs. No change in MICs to aminoglycosides and other antibiotics, acriflavine, and triclosan, was observed for the ΔemrE mutant, suggesting the primary role of EmrE in Lm is to increase its tolerance of QACs. Overall, findings from this research provide evidence that differences in stress survival and virulence potential exist among food chain-derived Lm. However, better understanding of the pressures occurring in FPEs that may contribute to strain persistence, and co-selection of antibiotic and sanitizer resistance mechanisms is needed.

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Attribution-NonCommercial-NoDerivs 2.5 Canada