Antimicrobial susceptibility of nisin resistant Listeria monocytogenes of dairy origin

The antibiotic susceptibility of wild Listeria monocytogenes strains and their corresponding nisin resistant variants was assessed. The resistant strains were more sensitive to most of the tested antibiotics than their wild-type counterparts. A slight increase in MIC was observed for a few antibiotics including the membrane disturbing polymixin B. Cross-resistance was detected with two synthetic antimicrobial peptides. A lower C15/C17 ratio in the membrane fatty acid composition of the nisin resistant strains was found, and one strain pair showed a significant difference in surface hydrophobicity. As judged by these results, no clear correlation could be established between resistance to nisin and to worldwide-used antibiotics.