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°C for C. albicans and T. glabrata , and after 48 h at 34°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 .