Antifungal susceptibility of Cryptococcus neoformans and Cryptococcus gattii isolates from decayed wood of trunk hollows of Ficus religiosa and Syzygium cumini trees in north-western India

Abstract

We present antifungal susceptibility data on environmental isolates of Cryptococcus neoformans (serotype A, n = 117) and Cryptococcus gattii (serotype B, n = 65) cultured from decayed wood of trunk hollows of Ficus religiosa and Syzygium cumini trees. Susceptibilities to amphotericin B, fluconazole, ketoconazole, itraconazole and voriconazole were determined by using Etest. The MICs were read after 48 h as per the guidelines provided by the manufacturer. The MIC₉₀s and susceptibility ranges for C. neoformans isolates were as follows: 0.094 (0.004–0.25) mg/L for amphotericin B, 4 (0.032–12) mg/L for fluconazole, 0.094 (0.004–0.75) mg/L for itraconazole, 0.064 (0.002–0.19) mg/L for ketoconazole, and 0.047 (0.006–0.125) mg/L for voriconazole, whereas for C. gattii isolates these were 0.125 (0.023–0.5) mg/L for amphotericin B, 8 (0.032–16) mg/L for fluconazole, 0.75 (0.006–2) mg/L for itraconazole, 0.125 (0.003–0.19) mg/L for ketoconazole, and 0.094 (0.004–0.125) mg/L for voriconazole. A comparison of the geometric means of MICs (mg/L) revealed that C. gattii was less susceptible than C. neoformans to amphotericin B (0.075 versus 0.051, P = 0.0003), fluconazole (2.912 versus 2.316, P = 0.003), itraconazole (0.198 versus 0.0344, P < 0.0001), ketoconazole (0.072 versus 0.037, P < 0.0001), and voriconazole (0.045 versus 0.023, P < 0.0001). The antifungal susceptibility data obtained in this study indicate that the occurrence of primary resistance among environmental isolates of C. neoformans serotype A and C. gattii serotype B is rare, and serotype B isolates are less susceptible than serotype A isolates.