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Abstract
Concerns over Listeria monocytogenes and its antimicrobial resistance are increasing for the food industry. Twenty isolates of L. monocytogenes were evaluated in this study for their resistance to three membrane perturbing antimicrobials - nisin, monensin, and gramicidin. Isolate ILSI NA 39, with similar susceptibilities to each antimicrobial, was further studied. The relationship of induced resistance to the other antimicrobials activity was determined by comparing growth of wild type and resistant strains in the presence of each antimicrobial at 10oC. Gramicidin manifested the lowest MIC against wild type and resistant ILSI NA 39 strains. Monensin was effective in agar MIC studies but not in broth studies. A slight genetic alteration (indicated by PFGE analysis) appeared in nisin resistant strains, while membrane protein differences (indicated by SDS-PAGE) occurred in gramicidin resistant strains. Further genomic, proteomic and lipid membrane studies are required to further describe relationships of the strains to the three antimicrobials.