Two nystatin-resistant mutants of Candida were isolated in vivo and identified as C. albicans and C. krusei. Analysis of the sterol composition of these cells indicated a total absence of ergosterol and an increased level of a possible precursor. Successive cultures of the resistant strains in a medium supplemented with 10 microgram ergosterol ml-1 induced in 5d a sensitivity to nystatin identical to that of the wild-type strain. These ergosterol-supplemented strains had an ergosterol content similar to that of the wild-type strain cultured in the absence of ergosterol. Resistance to nystatin was recovered after 5d subculture in medium without ergosterol.
