Modifications of membrane phospholipid composition in nisin-resistant Listeria monocytogenes Scott A

Abstract

A nisin-resistant (NIS(r)) variant of Listeria monocytogenes Scott A was isolated by stepwise exposure to increasing concentrations of nisin in brain heart infusion (BHI) broth. The NIS(r) strain was about 12 times more resistant to nisin than was the wild-type (WT) strain. Accordingly, higher nisin concentrations were required to dissipate both components of the proton motive force in the NIS(r) strain than in the WT strain. Comparison of the membrane fatty acyl composition of the sensitive strain with that of its NIS(r) derivative revealed no significant differences. From phospholipid head group composition analysis and phospholipid biosynthesis measurements during growth in the absence and presence of nisin, it could be inferred that the NIS(r) strain produces relatively more phosphatidylglycerol (PG) and less diphosphatidylglycerol (DPG) than the parent strain does. Monolayer studies with pure lipid extracts from both strains showed that nisin interacted more efficiently with lipids derived from the WT strain than with those derived from the NIS(r) strain, reflecting qualitative differences in nisin sensitivity. Involvement of the cell wall in acquisition of nisin resistance was excluded, since the WT and NIS(r) strains showed a comparable sensitivity to lysozyme. Recently, it has been demonstrated that nisin penetrates more deeply into lipid monolayers of DPG than those of other lipids including PG, phosphatidylcholine, phosphatidylethanolamine, monogalactosyldiacylglycerol, and di-galactosyidiacylglycerol (R. A. Demel, T. Peelen, R. J. Siezen, B. de Kruijff, and O. P. Kuipers, Eur. J. Biochem. 235:267-274, 1996). Collectively, the mechanism of nisin resistance in this L. monocytogenes NIS(r) strain is attributed to a reduction in the DPG content of the cytoplasmic membrane.