Introduction: Since the advent of standardized antifungal susceptibility testing for Candida albicans, efforts have been made to identify the molecular correlates of azole resistance. While overexpression of efflux pumps such as CDR1 and CDR2 have been shown by Northern blot analysis to correlate with in vitro resistance, a significant number of resistant strains have no identifiable molecular marker of resistance. These analyses have largely been performed using strains grown under standard laboratory culture conditions, which vary dramatically from those used during susceptibility testing. We hypothesized that the expression of azole resistance genes may differ dramatically according to culture conditions. Methods: Clinical isolates of C. albicans with varying susceptibilities to multiple azoles were grown in both standard culture conditions (YEPD medium at 30Â°C, mid-log growth phase) and conditions approximating the NCCLS antifungal susceptibility testing method (RPMI+MOPS medium plus L-glutamine and 1/2-MIC of azole antifungal, 37Â°C for 24 hrs). Itraconazole and the triazole CS-758 were tested. Total RNA was extracted from cultures and the expression of drug resistance genes examined using Northern blot analysis. Results: Expression of both CDR1 and CDR2 were observed to be significantly upregulated during growth under the NCCLS testing conditions. In contrast, expression of both these genes was nearly undetectable during standard testing conditions. The specific degree of CDR gene expression differed both by strain and by azole tested. For the majority of strains, induction of both CDR1 and CDR2 expression was more marked with itraconazole than with CS-758. Conclusions: Testing for the molecular markers of azole drug resistance should be done under conditions that best mimic the growth conditions used for in vitro susceptibility testing. CS-758 may have a decreased propensity to up-regulate CDR1 and CDR2 in vitro.
Full conference title:
42nd Interscience Conference on Antimicrobial Agents and Chemotherapy
- ICAAC 42nd