Effect of the lipid composition of Mycoplasma mycoides subspecies capri and phosphatidylcholine vesicles upon the action of polyene antibiotics.

(1) The effects of filipin and amphotericin methyl ester upon the K+ efflux from Mycoplasma mycoides subsp. capri and egg lecithin sonicated vesicles were investigated. Both the nature of the sterol and the composition of the membranes affected the sensitivity to each polyene antibiotic. (2) M. mycoides subsp. capri containing ergosterol was much more sensitive to amphotericin methyl ester than cells containing cholesterol. Cholesterol-containing cells were about twice as sensitive to filipin as the ergosterol-containing cells. These results were confirmed with phosphatidylcholine vesicles. (3) At 2 degrees C the filipin sensitivity of M. mycoides subsp. capri was independent of the membrane cholesterol content and the sensitivity towards amphotericin methyl ester decreased when the membrane cholesterol content was increased, in contrast to the results at 20 degrees C. (4) At 2 degrees C, sterol-free egg lecithin vesicles became very sensitive to both filipin and amphotericin methyl ester and the presence of cholesterol in the vesicles did not increase the sensitivity further. At high concentrations of cholesterol (greater than 30 mol%), the polyene antibiotic sensitivity, particularly towards amphotericin methyl ester, was greatly reduced.