In vitro antifungal susceptibility testing of Candida blood isolates and evaluation of the E-test method

Jang-Jih Lu, Shih-Yi Lee, Tzong-Shi Chiueh
Division of Clinical Pathology, Department of Pathology, Tri-Service General Hospital, Taipei, Taiwan, ROC

Received: February 23, 2004 Revised: March 31, 2004 Accepted: June 25, 2004

Corresponding author: Jang-Jih Lu, M.D., Ph.D., Division of Clinical Pathology, Department of Pathology, Tri-Service General Hospital, No. 325, Section 2, Cheng-Kung Rd., Taipei, Taiwan, ROC. E-mail:

Fungal infections have dramatically increased in recent years, along with the increase of drug-resistant isolates in immunocompromised patients. Ninety eight Candida species obtained from blood cultures at the Tri-Service General Hospital, Taiwan, from 1998 to 2000 were studied. These included 50 Candida albicans, 13 Candida glabrata, 24 Candida tropicalis and 11 Candida parapsilosis isolates. To investigate their susceptibility to commonly used antifungal drugs, minimum inhibitory concentrations (MIC) of amphotericin B, fluconazole, flucytosine, and ketoconazole were determined. Both the National Committee for Clinical Laboratory Standards reference broth macrodilution method and E-test were used in parallel. Ninety five isolates (95/98, 96.94%) were susceptible to amphotericin B at a concentration <1 g/mL. All isolates (100%, 98/98) were susceptible to flucytosine. Approximately 30% of these Candida isolates were resistant to fluconazole. The MIC for 90% of isolates (MIC₉₀) values for both methods for these isolates were 0.5 g/mL for amphotericin B, 32 g/mL for fluconazole, 0.25 g/mL for flucytosine (0.125 g/mL by E-test method), and 4 g/mL for ketoconazole. MIC for 50% of isolates (MIC₅₀) values for these agents were 0.25, 2, 0.06, and 0.06 g/mL, respectively. The essential agreement of MIC values within 2 dilutions for the 2 methods was 99.0% for amphotericin B, 90.8% for ketoconazole, 92.9% for fluconazole, and 91.8% for flucytosine. This study showed that E-test has equivalent performance to the broth macrodilution method and can be used as an alternative MIC technique for antifungal susceptibility testing.

Key words: Antifungal agents, culture media, microbial sensitivity tests, reference standards

J Microbiol Immunol Infect 2004;37:335-342.