Date of Award
Honors College Thesis
Janet Donaldson, Ph.D.
Salmonella is a gram negative, facultative anaerobic food borne pathogen and is the leading cause of deaths related to food borne illnesses. In order to establish an infection successfully, Salmonella must be able to survive in the presence of various stressors that it encounters, namely changes in pH, oxygen availability, osmolarity and bile. Previous research has shown that exposure to bile causes a shift in fatty acid composition in the cell membrane of the enteric bacterium Enterococcus faecalis. Thus, this led to the hypothesis that Salmonella incorporates fatty acids into its cellular membrane following exposure to bile and thereby protects itself against bile induced damage. To determine what effect bile has on the fatty acids in the membrane of Salmonella and if this shift has a direct link to bile resistance, fatty acid profiles of four strains of Salmonella (S. Heidelberg, S. typhimurium, S. typhi, and S. enteritidis) were examined using fatty acid methyl esters (FAME) analysis following exposure to either 0% bile or 0.3% bile. Following exposure to bile, there was a change in the fatty acid profile in all four strains. The fatty acids that increased across all four strains were the unsaturated fatty acids oleic acid and linoleic acid. The saturated fatty acid palmitic acid increased in all strains except S. enteriditis. To determine if the incorporation of these fatty acids contributed to bile resistance, cultures were pre-treated with a lipid mix containing varying concentrations of lipid mix (Sigma L0288) and then exposed to 0% and 5% bile for 1 hour, and the viability was assessed using plate counts. Data from the survival analysis showed that the lipid mix had no impact on survival after bile exposure. This study shows that the fatty acid profile of Salmonella changed after exposure to bile and that these changes in the fatty acid profile did not correlate with increased bile survival of Salmonella. Further work is needed to determine how this impacts the ability of Salmonella to cause salmonellosis.
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Redfern, Betsy H., "The Incorporation of Lipids into the Cellular Membrane of Salmonella" (2019). Honors Theses. 678.