Comparative study of in vitro methods to analyse the antifungal activity of propolis against yeasts isolated from patients with superficial mycoses

AIM: To test a total of 15 strains belonging to four species of yeasts by different in vitro methods against propolis and itraconazole (ITC). METHODS AND RESULTS: Three methods were compared for susceptibility testing of yeast isolates to propolis: disc diffusion method, agar dilution method and National Committee for Clinical Laboratory Standards (NCCLS, M27A) broth microdilution method. ITC was selected as the antifungal agent for comparison study. Using the broth microdilution method, the geometric mean for MIC (microg ml(-1)) with regard to all isolates was < or =0.06 for propolis and < or =0.35 for ITC. The broth microdilution and the agar dilution methods were in good agreement (75%) for propolis against yeasts isolated from patients with superficial mycoses. Using the diffusion method, all strains showed a broad zone of inhibition at the first available reading time (24 or 48 h). An increase of MIC values was accompanied by a decrease of growth inhibition zone diameter. A favourable correlation was found between MIC and inhibition zone around the disc for propolis sample and the correlation coefficient was: r = -0.626 (P < 0.01). CONCLUSIONS: This study suggests the potential value of the agar dilution and disc diffusion method as a convenient alternative method for testing of yeasts to propolis. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated that propolis and ITC were very active against yeasts from patients with superficial mycoses. The other prominent finding in this study is that RPMI 1640 with L-glutamine was the available broth for the in vitro susceptibility testing of yeasts.