Lactococcus lactis subsp. cremoris JFR1 Suppresses Virulence Gene Expression Of Salmonella In Intestinal Epithelial Cells

Date and Time

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Canadian Research Institute for Food Safety (CRIFS) Boardroom

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DEFENCE ANNOUNCEMENT
Final Examination for the Degree of PhD Food Science  - JUSTINA ZHANG

Examining Committee
Dr. Jeff Farber, Chair
Dr. Gisele LaPointe, Advisor
Dr. Milena Corredig, Co-Advisor
Dr. Yoshi Mine, Department Member
Dr. Patricia Ruas-Madiedo, External Examiner

TITLE: LACTOCOCCUS LACTIS SUBSP. CREMORIS JFR1 SUPPRESSES VIRULENCE GENE EXPRESSION OF SALMONELLA IN INTESTINAL EPITHELIAL CELLS

ABSTRACT: A major foodborne pathogen, Salmonella enterica subsp. enterica serovar Typhimurium, causes disease in humans by expressing virulence genes to invade the host epithelial cells. Interactions between food or food components, pathogens, and the host environment could alter the fate of pathogen colonization. Thus, the search for food/food components bearing antivirulence properties could contribute to the reduction of Salmonella invasion. This research revolves around utilizing Lactococcus lactis subsp. cremoris JFR1 (JFR) treatments on intestinal epithelial cells to determine the effects on Salmonella invasion and virulence properties. Comparisons of JFR exopolysaccharide producing and nonproducing strains demonstrated that both strains could down regulate the virulence gene expression and reduce attachment of Salmonella to HT-29 epithelial cells. However, further analysis utilizing exopolysaccharides extracted from JFR revealed that there was no significant effect on Salmonella virulence gene expression or attachment onto HT29 epithelial cells at the concentrations ranging between 0-0.2 mg/mL. In intestinal epithelial cell models comprised of mucus producing cells (HT29-MTX), absorptive type cells (Caco-2) and cocultures, JFR treatments of epithelial cells suppressed and reduced invasion of only Salmonella Typhimurium DT104 but not Salmonella lacking OppA. This was also demonstrated when milk fermented with JFR strains were applied to epithelial cells. Suppression of Salmonella virulence, lower numbers of invasive bacteria as well as reduced epithelial cell production of inflammatory cytokine and higher transepithelial electrical resistance was observed only when infected by S. Typhimurium DT104. Infection of epithelial cells by S. Typhimurium mutant ΔoppA was unresponsive to treatments applied and did not show differences in virulence and invasion compared to controls. Furthermore, treatments of epithelial cells by digested of JFR fermented milk treatments lost its ability to suppress virulence genes in both Salmonella strains, regardless of a functional OppA. These results indicate the importance of OppA and its role in virulence gene suppression in the presence of JFR treatments. A possible mode of action could be the presence of peptides, of a certain length, in JFR treatments which harbour antivirulence properties perhaps by acting as quorum sensing inhibitors or interacting directly with the enzyme responsible for autoinducer production.

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