Background: Azoles constitute an important class of antifungal agents widely used in both agriculture and clinical medicine. Their efficacy is often limited by a variety of biological processes. Among these, the overexpression of membrane efflux pumps of the ABC (ATP-binding cassette) and MF (major facilitator) families, which lower intracellular drug concentration below effective levels, is a major but complex mechanism that results in multidrug resistance (MDR). MDR is considered to be the major challenge for modern chemotherapy. Methods: Here we describe the cloning and characterization of AzoA, which is a novel molecular determinant of sensitivity to azoles in aspergillus nidulans. This gene was identified from an azole-hypersensitive mutant of A. nidulans, obtained by insertion mutagenesis followed by plasmid rescue. Results: Blast analysis of AzoA revealed similarity to hypothetical proteins with unknown function from yeasts and other pathogenic fungi. Northern analysis revealed increased transcript levels of azoA upon treatment of fungal germlings with azoles. Gene-replacement mutants of azoA, also displayed increased sensitivity to azoles, confirming its functional role. Interestingly, transcript levels of the ABC transporter atrG, a previously characterized efflux pump involved in protection of A. nidulans against azoles is higher in delta-azoA mutants. Additionally, all delta-azoA mutants displayed LOWER accumulation of [14C]fenarimol, as compared to a control strain Conclusions: Lower accumulation of compounds is expected on MDR fungi, e.g. reduced intracellular accumulation due to overexpression of efflux pumps (AtrG). The phenotype observed for delta-azoA mutants is increased sensitivity to azoles but with a lower intracelular accumulation. These results suggest a major role for azoA on regulation of MDR pumps and on fungal sensitivity to azoles.
Full conference title:
43rd Interscience Conference on Antimicrobial Agents
- ICAAC 43rd