In vitro susceptibility of mycelial and yeast forms of Penicillium marneffei to amphotericin B, fluconazole, 5-fluorocytosine and itraconazole

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Abstract
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. marnefei'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.