EFFECT OF CHOLESTEROL ON THE SENSITIVITY OF MYCOPLASMA LAIDLAWII TO THE POLYENE ANTIBIOTIC FILIPIN.

Weber, Morton M. (St. Louis University School of Medicine, St. Louis, Mo.), and Stephen C. Kinsky. Effect of cholesterol on the sensitivity of Mycoplasma laidlawii to the polyene antibiotic filipin. J. Bacteriol. 89:306-312. 1965.-The polyene antibiotic, filipin, inhibited growth and caused lysis of Mycoplasma laidlawii cells which had been cultured in the presence of cholesterol. The antibiotic did not inhibit growth and did not promote lysis of the organism when grown in the absence of cholesterol. These results constitute strong support for the contention that the presence of sterol in the cell membrane is a necessary prerequisite for polyene sensitivity. Higher concentrations of filipin were required to inhibit growth when serum was added to the assay medium than when it was absent. These results suggest binding of the antibiotic to some component in the serum and may partially account for the previous inability to demonstrate growth inhibition by low concentrations of the polyene antibiotics. The extent of growth inhibition due to filipin decreased upon prolonged incubation. Subculture in the presence of high concentrations of antibiotic indicated that the apparent reversal of inhibition was caused by emergence of a filipin-resistant cell population. It was also observed that cells, which originally were rapidly lysed by filipin and digitonin, were no longer responsive to the action of these agents upon incubation in sterol-free medium at 25 or 37 C for several hours. This effect could be prevented by keeping the cells at 2 C. These results may indicate that filipin-resistant cells carry out a metabolic conversion of membrane-localized sterol to a form which can no longer react with the antibiotic. Other possible causes of resistance, which cannot be excluded on the basis of the present data, are discussed.