Action of polymyxin B on bacterial membranes: phosphatidylglycerol and cardiolipin induced susceptibility to polymyxin B in Acholeplasma laidlawii B

Abstract

To identify the polymyxin receptor molecules in the membranes of living microorganisms, fusion of intact A. laidlawii B with lipid vesicles was investigated according to the procedure of Grant and McConnell (1973). The naturally polymyxin resistant A. laidlawii B was treated with phospholipid vesicles prepared from purified phospholipids of the polymyxin susceptible Salmonella typhimurium G30. A. laidlawii B absorbed between 15 and 45% of its own lipid content of the added tritium labeled phospholipids without loss of viability. Association with the acidic components phosphatidylglycerol and cardiolipin produces a 10 to 30 fold increase in polymyxin susceptibility, which was not obtained with egg phosphatidylcholine and mixed phosphatidylcholine phosphatidylethanolamine vesicles. The polymyxin sensitized cells bound 12 times more radioactive antibiotic than resistant cells. The phosphatidylglycerol induced susceptibility was abolished by serum fraction V (Cohn) proteins.