Korean J Lab Med.  2002 Jun;22(3):188-195.

Evaluation of a Spectrophotometric Broth Microdilution Method for Determining Fluconazole Susceptibility of Candida albicans: Influence of RPMI and RPMI-2% Glucose on the Selection of Endpoint Criteria

• Yi JY
• Shin JH
• Lee KW
• Yong DE
• Yang SJ
• Suh SP
• Ryang DW

Abstract

BACKGROUND: Minimum inhibitory concentration (MIC) endpoint determination is the major varia-tion source for the fluconazole susceptibility test, especially for Candida albicans. In this study, we evaluated spectrophotometric broth microdilution methods using RPMI 1640 and RPMI supple-mented with 18 g of glucose per liter (RPMI-2% glucose) for determining fluconazole susceptibility of C. albicans.
METHODS
A total of 129 clinical isolates of C. albicans were tested by the broth microdilution method using RPMI and RPMI-2% glucose. The MIC endpoint was calculated objectively with the spectrophotometer set at 405 nm. These results were compared to those by the National Commit-tee for Clinical Laboratory Standards (NCCLS) macrodilution method and the agar dilution method.
RESULTS
The mean absorbances in the drug-free wells in RPMI and RPMI-2% glucose were 0.208 +/- 0.014 and 0.316 +/- 0.061, respectively, at 24 h and 0.339 +/- 0.094 and 0.530 +/- 0.104, respectively, at 48 h (P < 0.01). The agreement of the microdilution method with the RPMI within two doubling dilutions of the macrodilution reference were 91.5% (118/129) at 24 h and 76.7% (99/129) at 48 h. The percentage of agreement in the microdilution method with the RPMI-2% glucose were significantly higher: 100% (129/129) at 24 h and 99.2% (128/129) at 48 h (P < 0.01). In addition, the MIC endpoints were easier to detect in RPMI-2% glucose, because of the greater difference in absorbance in between grown wells and fluconazole-inhibited wells (P < 0.01).
CONCLUSIONS
The spectrophotometric microdilution method with RPMI-2% glucose may have an excellent agreement with the NCCLS broth macrodilution method and may provide more easily determined MIC endpoints for fluconazole susceptibility testing for C. albicans.

Keyword

Spectrophotometric broth microdilution method; Fluconazole; Candida albicans; RPMI-2% glucose

MeSH Terms

Agar
Candida albicans*
Candida*
Endpoint Determination
Fluconazole*
Glucose*
Microbial Sensitivity Tests
Agar
Fluconazole
Glucose