Antifungal activity upon Saccharomyces cerevisiae of iturin A, mycosubtilin, bacillomycin L and of their derivatives; inhibition of this antifungal activity by lipid antagonists.

The antifungal activity of three antibiotics of the iturin group: iturin A, mycosubtilin, bacillomycin L and of eleven methylated and acetylated derivatives of these antibiotics was tested upon Saccharomyces cerevisiae. The lowest MIC values were found for natural antibiotics. The substitution of polar groups diminished the antifungal activity. Various lipids, sterols, fatty acids, fatty acid methyl esters and phospholipids were tested as inhibitors of the antifungal activity of iturin A, mycosubtilin and bacillomycin L. Cholesterol was the strongest inhibitor upon the three antibiotics; ergosterol, oleic acid and cis-vaccenic acid were less potent inhibitors. Among phospholipids, phosphatidyl choline inhibited bacillomycin L and iturin A while diphosphatidyl glycerol inhibited bacillomycin L and mycosubtilin. The inhibitory effect appeared to be dependent on the nature of both the hydrophilic group and the fatty acid part of phospholipids.