Comparative study of susceptibilities of germinated and ungerminated conidia of Aspergillus fumigatus to various antifungal agents

Conidia are used as inocula for the in vitro susceptibility testing of Aspe rgillus fumigauts. Since the MIC is defined on the basis of visible mycelia l growth, conidia should germinate and produce sporelings (germinated conid ia) for monitoring of the growth inhibition and fungicidal activity of a dr ug, If a compound is capable of inhibiting germination of conidia while aff ecting or not affecting the growth of the organism, the MIC obtained will b e the concentration of the drug required for the inhibition of conidial ger mination but not necessarily that required for inhibition of the growth of the organism. We investigated the susceptibility of germinated and ungermin ated conidia to amphotericin B, itraconazole, voriconazole, and SCH56592, T he MICs of various antifungal agents for germinated conidia were almost ide ntical to those obtained for ungerminated conidia. In addition, both the ge rminated and ungerminated conidia were killed with almost equal efficiency by all of the compounds tested when exposed to the drugs for 24 h, These re sults suggest that either germinated or ungerminated conidia could be used as inocula for in vitro susceptibility studies of. A. fumigatus with identi cal results.