In vitro antifungal susceptibility of Candida

To develop a simple, standardised procedure for antifungal susceptibility of yeasts, disc diffusion test was evaluated in comparison to agar dilution and the macrobroth dilution procedure of the National Committee for Clinical Laboratory Standards USA. One hundred Candida strains isolated from clinical material were used against four antifungal agents (amphotericin B, 5-flucytosine, ketoconazole and fluconazole). Inoculum size of 10(6) yeasts/ml just failed to produce confluent colonies at 37 degrees C after 48 h on yeast nitrogen-glucose-agar with or without asparagine medium. The zones of inhibition were correlated with both broth and agar dilution minimum inhibitory concentrations (MICs). The results were found to correlate well using amphotericin B, 5-flucytosine and fluconazole (with broth dilution only). But there was no significant correlation using ketoconazole. Therefore, disc diffusion susceptibility testing of Candida strains appears to be generally applicable except for azoles where broth dilution test would confirm the resistant isolates.