Chemical alterations in cell envelopes of polymyxin-resistant mutants of Pseudomonas aeruginosa grown in the absence or presence of polymyxin

The polymyxin-resistant mutant strains H181 and H185 of Pseudomonas aeruginosa, after growth in the absence or presence of polymyxin, were compared with the polymyxin-sensitive H103 strain as to their cell envelope protein composition (determined by slab polyacrylamide gel electrophoresis) and their lipid composition. When grown in the absence of polymyxin, the H181 and H185 strains had an increased content of the outer membrane protein H1 with a decreased content of the outer membrane proteins D2 and F. After growth in the presence of polymyxin, the content of H1, D2, and F were all decreased. Significant alterations in the lipid composition of the H181 and H185 strains were found after growth in the absence of polymyxin. These lipid alterations were enhanced upon growth in the presence of polymyxin, with both strains having a reduced content of phosphatidylethanolamine and phosphatidylglycerol and an increased content of diphosphatidylglycerol and an unidentified lipid thought to be a neutral lipid. Other workers have proposed that an increased content of H1 protein is the molecular basis for polymyxin resistance in the H181 and H185 strains. Our observations make this hypothesis appear unlikely.