In vitro Susceptibility of Mycelial and Yeast Forms of Penicillium marneffei to Amphotericin B, Fluconazole, 5-Fluorocytosine and Itraconazole

The mycelial (25°C) and yeast-like (37°C) forms of Penicillium marneffei clinical and type strains were investigated for their in vitro susceptibility to amphotericin B (AmB), 5-fluorocytosine (5-FC), fluconazole (FLU) and itraconazole (ITZ), using Bacto antibiotic medium 3, yeast-nitrogen, Sabouraud's dextrose (pH 5.7) and high resolution (pH 7.1) broth media (1ml/tube), respectively. Results indicated that the minimal inhibitory and minimal fungicidal concentrations (MICs and MFCs) for the mycelial cultures of P. marneffei to AmB were in the range 0.78-1.56 and 0.78-3.125 μg/ml, respectively, as against 3.125-25 μg (MICs) for the yeast form cultures. The MFCs to AmB for the yeast form were one dilution higher. The MICs to FLU were generally lower for the yeast form (6.25-25 μg) than the mycelial form (25-50 μg/ml), whereas MFCs for the mycelial cultures were > 100 μg as compared to 6.25-100 μg for their yeast form. The MICs for the mycelial form to 5-FC ranged from < 0.195-0.39 μg. Higher MICs (6.25 μg) were recorded for their yeast form. The MFCs to 5-FC for the yeast form were 25-100 μg/ml. The MICs for the mycelial form to ITZ ranged from < 0.195 to 3.125 μg/ml. Higher values (< 0.195-50 μg) were recorded for their yeast-like form. The MFCs to ITZ for mycelial and yeast forms ranged from < 0.195-0.39 and 25-100 μg/ml, respectively. Results indicate that P. marneffei's yeast form is more sensitive to FLU and ITZ (8 of 10 strains) while the mycelial form displayed greater susceptibility to AmB and 5-FC. The MICs for ITZ remained steady in SD medium, pH 5.7 to 7.1. However, some strains gave higher MIC values (0.39-1.56 μg/ml) when tested in the HR.