Exploring comparative and transcriptomic analyses to unveil mechanisms of resistance to azoles dependent and independent of CgPdr1 in Candida glabrata clinical isolates

The pathogenic yeast species Candida glabrata has an intrinsically high resilience to azoles and a rapid capability of acquiring resistance. Azole-resistant clinical strains derive mostly from them encoding hyperactive mutants of the CgPdr1 regulator, however, strains encoding wild-type CgPdr1 variants were identified suggesting a role for CgPdr1-independent mechanisms in acquisition of resistance in vivo. Seven azole-resistant C. glabrata isolates were found to encode CgPdr1 gain-of-function variants, two, I392M and I803T, being herein described for the first time. OMICS profile of the sole azole-resistant strain encoding a wild-type CgPDR1 allele revealed that these cells over-express several genes described for providing protection against azoles, while down-regulating genes described to increase sensitivity to these drugs. Over-expression of genes required for metabolism and transport of sterols to compensate the azole-induced inhibition of Erg11 and a more active calcineurin pathway are other mechanisms suggested to underlie azole resistance in ISTB218. The Candida isolates were cultivated in RPMI medium (with 20 g/L as the carbon source) until mid-exponential phase after which they were harvested by centrifugation and immediately frozen until further processing for mRNA extraction and hybridisation in the microarray.