Quantitative evaluation of the antifungal properties of cycloheximide.

Although the total growth of both zoopathogenic and saprophytic fungi on cycloheximide media was consistently less than that on the control without the antibiotic, a progressive increase in the growth rate of these organisms occurred during exposure to the drug. The extent of this change depended upon the concentration of cycloheximide, the species and strain of the test organism, and the duration of exposure. Significant alterations were also observed in the macroscopic appearance of the colonies. The results of this investigation agree with those of previous studies regarding the value of cycloheximide in selective isolation media, but there were discrepancies with respect to the degree of sensitivity of several of the organisms studied. The increase in the rate of growth on cycloheximide media may indicate an induced adaptation to the drug.