摘要：

The role of lipid content of the cell envelope in the resistance of S. marcescens to polymyxin B was studied. Both the free lipid and the lipopolysaccharides were extracted from whole cells of sensitive and resistant strains, and the lipid compositions, including fatty acid content, were determined. No differences were observed for the contents of total extractable lipid, the phospholipids and their components. However, the yields of lipopolysaccharide and its glucosamine content were higher in resistant strains. The lack of observable differences in the fatty acid composition of the lipopolysaccharides seemed to indicate that the lipid A of lipopolysaccharide may not be involved in the mechanism of resistance to the antibiotic, but its role as the site of inactivation of endotoxin by polymyxin B should not be ignored. On the other hand, significant differences in the fatty acid composition of the extractable lipid fractions were observed. The sensitive strains had a higher proportion of unsaturated fatty acids, particularly in the phospholipid fraction. The results are consistent with the suggestion that an increase of unsaturated fatty acid in sensitive strains may facilitate penetration of polymyxin B to the site of lethal action. Conversely, an increased amount of saturated fatty acid in the resistant strains might promote more hydrophobic interactions with the hydrophobic site (6 methyloctanoic acid) of the polymyxin B and, hence, prevent the antibiotic from exerting its lethal action.

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