Vol.55 No.4 July 2007

Measurement of the minimal inhibitory concentrations and minimal fungicidal concentrations of antifungal agents against Candida strains isolated from blood cultures

Shin-ichi Fujita

Department of Laboratory Medicine, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa, Japan

Abstract

We measured the minimal inhibitory concentrations (MICs) and minimal fungicidal concentrations (MFCs) of micafungin (MCFG), amphotericin B (AMPH-B), flucytosine (5-FC), voriconazole (VRCZ), itraconazole (ITCZ), miconazole (MCZ), and fluconazole (FLCZ) for 57 Candida strains isolated by blood cultures. In the experiment of viable cell counting, polysorbate 80 was added to the sterile saline in order to inhibit the aggregation of fungus cells, and to Sabouraud agar media, in combination with lecithin and histidine, to overcome the carryover effect of antifungal agents. MFC was defined as the lowest concentration of the drug that could kill 99% of viable cells. The MFC₉₀ values of MCFG and AMPH-B for C. albicans (14 strains), C. tropicalis (11 strains), and C. glabrata (14 strains) were 0.03 and 1 μg/mL, 0.125 and 0.5 μg/mL, and 0.5 and 2 μg/mL, respectively. Furthermore, MCFG and AMPH-B exhibited superior fungicidal activity against azole-resistant C. albicans (one strain) and azole-resistant C. tropicalis (one strain). While the MIC₉₀ of VRCZ for 16 C. parapsilosis strains was 0.008 μg/mL, showing the greatest growth-inhibitory activity, the MFCs of VRCZ for C. parapsilosis ranged from 0.03 to ≥32 μg/mL, and the MFC₉₀ of VRCZ was 32 μg/mL or more. In contrast, AMPH-B and MCFG showed marked fungicidal activity, and the MFC₉₀ of AMPH-B and MCFG for C. parapsilosis was 2 and 8 μg/mL, respectively. As compared to MCFG, AMPH-B showed more marked fungicidal activity against two C. guilliermondii strains. The MFC₉₀ of the azoles for Candida strains belonging to the five Candida species isolated could not be defined at the concentrations tested. Our results demonstrated that MCFG and AMPH-B exhibit superior fungicidal activity against medically important Candida strains isolated by blood cultures.

Key word

Candida, MIC, MFC

Received

September 27, 2006

Accepted

April 20, 2007

Jpn. J. Chemother. 55 (4): 257-267, 2007