Comparative susceptibility of four kinds of pathogenic fungi to amphotericin B and amphotericin B methyl ester.

The activity of amphotericin B methyl ester was compared with that of amphotericin B, using Candida albicans (34 isolates), Torulopsis glabrata (12 isolates), Filobasidiella neoformans (stat. conid. Cryptococcus neoformans) (14 isolates), and Coccidioides immitis (37 isolates) and tube dilution in a totally synthetic, completely defined medium (SAAMF) with inocula of 10(4) colony-forming units per ml. Minimal inhibitory concentrations were read after 24 h at 34 degrees C for C. albicans and T. glabrata, and after 48 h at 34 degrees C for C. immitis and F. neoformans. Minimal lethal concentrations were determined by subculture of 10% of the volume of the cultures without evident growth onto Sabouraud glucose agar medium. Overall, amphotericin B methyl ester was slightly less active than amphotericin B, with the differences attaining statistical significance for: (i) inhibition of C. albicans and T. glabrata and (ii) killing of T. glabrata.