Lipids of antibiotic-resistant and -susceptible members of the Enterobacteriaceae.

Lipids of antibiotic-resistant and related -susceptible strains of the Enterobacteriaceae were extracted with chloroform-methanol and characterized by thin-layer chromatography, densitometry, and fatty acid analysis using gas chromatography. Quantitative differences which correlated with antibiotic resistance existed among the phospholipids and fatty acids. A relatively higher concentration of a ninhydrin-positive phospholipid concentration with a lower amount of phosphatidylethanolamine was observed in antibiotic-resistant strains of serratia marcescens. Bacterial strains which harbored R-factor 222 had a higher ratio of phosphatidylglycerol to diphosphatidylglycerol than their respective parent strains while those strains which were resistant to the polymyxins had a lower ratio of these phospholipids. Differences in the relative amounts of certain unsaturated and cyclopropane fatty acids were observed between susceptible and resistant strains. Such differences, however, were dependent upon a particular genus and species.