Broth microdilution (BMD) is a standard assay for susceptibility of Candida to antifungals, but complexity limits its routine application. E-test (ET) and disk diffusion (DD) assays are attractive alternatives because of their simplicity and reproducibility.
To determine the correlation between BMD, and ET and DD assay results for Candida isolates.
We tested 63 Candida isolates for their susceptibility to fluconazole and voriconazole using BMD, ET, and DD, and recorded minimum inhibitory concentrations (MIC) and inhibitory zone diameters (ZD). Spearman correlations were determined and the Clinical and Laboratory Standards Institute recommendations were used to assess major and minor errors in test results.
The isolates included 32 (51%) C. albicans, 14 (22%) C. tropicalis, 12 (19%) C. parapsilosis, 4 (6%) C. glabrata, and 1 (2%) C. guilliermondii. The BMD-MIC and ET-MIC had good correlation for fluconazole (r = 0.94; P < 0.001) and voriconazole (r = 0.95; P < 0.001). The BMD-MIC for both antifungals were significantly correlated with the ZD of the DD assays (r = −0.47; P < 0.001; r = −0.75; P < 0.001, respectively). Agreement between the BMD and the ET and DD results exceeded 90%. No major errors were identified in any comparisons.
C. albicans were predominant among the isolates and were susceptible to fluconazole and voriconazole. The BMD results were well correlated with ET and DD assay results, and therefore ET and DD assays can be recommended as initial screening tools in resource-limited hospitals because of their relatively low cost.