Missense mutation in CgPDR1 regulator associated with azole-resistant Candida glabrata recovered from Thai oral candidiasis patients

Abstract Objectives Non- albicans Candida (NAC) species are increasingly identified as pathogens causing oral candidiasis. Incidence rates for azole resistance among NAC species have been continuously reported. This study aimed to evaluate azole susceptibility profiles and characterize azole-resistance mechanisms of oral clinical NAC isolates. Methods In vitro susceptibility patterns of 85 Non- albicans Candida isolates were performed using the broth microdilution method. Azole resistance-related genes ( ERG3, ERG11 and PDR1 ) of Candida glabrata were sequenced to determine the presence of nucleotide substitutions. Expression levels of various resistance-related genes were also evaluated using qRT-PCR in azole-susceptible, susceptible dose dependent (SDD), and resistant Candida isolates. Results Two C. glabrata isolates (2.4% of all NAC isolates) were resistant to all three kinds of azoles (fluconazole, itraconazole, ketoconazole). All clinical isolates of C. tropicalis and C. kefyr were susceptible to azoles. Silent mutations were found in the CgERG11 and CgERG3 of clinical C. glabrata isolates. Interestingly, two missense mutations in CgPDR1 (N768D and E818K) were identified only in resistant C. glabrata isolates. The presence of CgPDR1 missense mutation in resistant isolates is associated with overexpression of its own product and multi-drug transporters including ABC transporters, MFS transporter. Conclusions A gain-of-function (GOF) mutation in CgPDR1 is associated with up-regulation of various drug transporters which appears to serve as primary mechanisms for azole resistance in the detected C. glabrata isolates. Therefore, analysis of GOF mutations in PDR1 regulator provides a better understanding of development of antifungal resistance.