The sensitivity of Listeria monocytogenes Scott A and ATCC 19114 to antimicrobial compounds was altered when bacterial membrane lipid composition was modified by growth in the presence of added fatty acids. Analysis of cellular fatty acid composition by gas-liquid chromatography indicated that L. monocytogenes Scott A cells contained 0.97, 2.32, 0.81, and 0.72% (relative) of C14:0, C16:0, C18:0, and C18:l, respectively. In the presence of exogenously supplied C14:0, C16:0, C18:0, and C18:l, the percentages increased to 14.03, 30.92, 16.30, and 27.90%. Average MICs for L. monocytogenes Scott A and ATCC 19114 to sodium chloride, tertiary butylhydroquinone, methyl paraben, and propyl paraben were 10.0%, 81, 1406, and 544 μg/ml, respectively. Growing either strain in the presence of 50 μg/ml of either exogenously added C14:0 or C18:0 fatty acids increased their resistance to the four antimicrobial compounds. However, growth in the presence of C18:1 led to increased sensitivity to the antimicrobial agents. The results indicate that the susceptibility of L. monocytogenes to antimicrobial agents is related to the lipid composition of the cell membrane. Consequently, food preservation processes which alter fatty acid composition of L. monocytogenes could result in changes in antimicrobial susceptibility.
1Present address: Eastern Regional Research Center. U.S. Department of Agriculture, Agricultural Research Service, Philadelphia, Pennsylvania 19118.
2*Present address: Department of Food Science, Toxicology, Food Research Center, University of Idaho, Moscow, Idaho 83843.
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