Involvement of the cell envelope of Listeria monocytogenes in the acquisition of nisin resistance

The involvement of the cell wall in the acquisition of nisin resistance by Listeria monocytogenes F6861 and its nisin‐resistant mutant was investigated. Results indicated that without a cell wall, the acquired nisin resistance of the mutant was lost. Cell surface hydrophobicity was shown to correlate with nisin sensitivity; the wild type strain being more hydrophobic than its mutant. The possible role of S‐layer proteins in nisin resistance was investigated. Examination of strains by freeze‐etching and atomic force microscopy did not demonstrate the presence of S‐layers in either strain while SDS‐PAGE following S‐layer extraction procedures revealed no major protein bands. Chloramphenicol did not adversely affect the frequency of isolation of nisin‐resistant mutants, indicating that de novo protein synthesis was not involved. The involvement of other cell surface components, teichoic and lipoteichoic acids, was also examined. In contrast with other reports, comparison of the total phospholipid content of the mutant with its parental strain showed no significant difference (P > 0.05).