Different culture media applied to the study of Cryptococcus neoformans susceptibility to amphotericin B and fluconazole

Abstract

This study compared the performance of three culture media used for the determination of minimal inhibitory concentration (MIC) of amphotericin B and fluconazole against 48 Cryptococcus neoformans strains. For amphotericin B the media employed were RPMI 1640 medium, as indicated by NCCLS as reference, Yeast Nitrogen Base (YNB) as proposed by Ghannoum et al. (YNB-1), Antibiotic medium 3 (AM3) indicated by others, and YNB as proposed by us (YNB-2). In YNB-1, amphotericin B showed broader MIC ranges, varying from 0.125 µg/ml to 1.0 µg/ml; in RPMI 1640 medium and YNB-2 the MICs were similar and in AM3 the MIC ranges were narrower. The same pattern was observed for MIC 90%. For fluconazole the media employed were RPMI 1640 and YNB-1. The MIC ranges were broader and elevated when YNB-1 was employed. MIC 50% were 2.0 µg/ml in RPMI 1640 medium and 4.0 µg/ml in YNB-1. Our results indicate that RPMI 1640 supplemented with 2% glucose allowed a good growth at 48h; YNB as recommended by Ghannoum et al. provided a broader MIC range, AM3 provided a narrow MIC range for amphotericin B, and YNB-2 was very similar to RPMI 1640 medium.

Susceptibility to heat and antifungal agents of Cryptococcus neoformans var. neoformans (serotype D) isolated from Eucalyptus spp in Rio Grande do Sul, Brazil

“…YNB-1 resulted in a broader MIC range, though amphotericin B resistant strains were not detected. These results are similar to those already obtained from clinical strains of C. neoformans serotype A using the same media (2).…”

“…The reference M27-A2 method based on RPMI 1640 medium has been used to test C. neoformans isolates (1,2,10,20). In spite of this indication, some previous reports suggested that RPMI 1640 medium did not support suitable growth of C. neoformans.…”