Abstract:
LY303366 (LY) is an investigational echinocandin that has demonstrated activity against Candida species. We attempted to isolate an LY resistant mutant by plating the C. albicans clinical strain Y41 at a concentration of 10$\sp7$ CFU/plate on Brain Heart Infusion agar (BHI) plates supplemented with LY at concentrations of 1 to 40 $\mu$g/ml. After 7 days of incubation at 35$\sp\circ$C very small colonies were observed. One colony was selected and repeatedly subcultured on BHI with 1 $\mu$g/ml LY. After 5 passages the MIC was demonstrated to be 1.28 $\mu$g/ml LY, (wild type MIC = 0.04 $\mu$g/ml, an increase of 32$\times$). However, when 6 colonies were individually subcultured to Sabouraud dextrose agar (SDA) plates, only 3 remained resistant to LY. One of the transient mutant strains was evaluated in terms of: antifungal susceptibility (amphotericin B, 5-flucytosine, fluconazole, ketoconazole), growth, stability, and pharmacodynamic time-kill curves. There were no differences observed between parent and transient mutant strains in antifungal susceptibility, or growth patterns. Transient resistant strains reverted back to the parent MIC after 3 passages on SDA. The resistance phenotype was restored when this strain was cultured on BHI with 1 $\mu$g/ml LY. The transient resistant strain exhibit regrowth during pharmacodynamic time-kill curves at 1$\times$ MIC of LY after this strain had reverted to the wild type MIC. One of the stable mutant strains was evaluated in terms of: antifungal susceptibility (amphotericin B, 5-flucytosine, fluconazole, ketoconazole), morphology, growth, stability, pharmacodynamic time kill-curves, and germ tube formation. (Abstract shortened by UMI.)
