Mechanism of azole resistance in Candida glabrata isolates from India: clinical vs. induced perspectives

<b>Introduction.</b> <i>Candida glabrata</i> is a pathogenic yeast in humans, recognized for its genomic plasticity and increasing prevalence of antifungal resistance, including multidrug-resistant phenotypes, especially in the US and European countries.<b>Hypothesis.</b> This study hypothesizes that the resistance mechanisms in clinically resistant strains of <i>C. glabrata</i> differ from laboratory-generated resistant strains.<b>Aim.</b> This study aims to understand the resistance mechanism in Indian clinical isolates of <i>C. glabrata.</i> <b>Methodology.</b> A total of 240 clinical isolates of <i>C. glabrata</i> were tested for antifungal susceptibility and one resistant strain was artificially synthesized in the laboratory. Both clinical and lab-generated resistant strains were analysed for antifungal resistance using methods such as phenotypic assays, real-time quantitative PCR, Fluorescence-activated cell sorting (FACS) analysis and targeted gene sequencing. Mechanisms involving drug efflux pumps, mismatch repair pathways, ergosterol biosynthesis pathway and biofilm formation were systematically studied.<b>Results.</b> Among clinical isolates, one susceptible-dose dependent strain and three fluconazole-resistant strains were identified. Both clinical and lab-generated resistant strains demonstrated antifungal resistance phenotypically, with increased expression of <i>CDR1</i>. Targeted gene sequencing revealed novel mutations in <i>PDR1</i>, while mutations in <i>MSH2</i> served as genotypic markers for resistance. Overexpression of <i>ERG11</i> was seen in a lab-generated resistant strain where a specific mutation was identified. Biofilm activity contributed to resistance in one of the clinical strains.<b>Conclusion.</b> This study reports for the first time the fluconazole resistance mechanism in <i>C. glabrata</i> from India. The findings underscore the diversity of resistance mechanisms among clinical and lab-generated isolates, emphasizing the need for novel antifungal therapies to address these emerging resistance profiles effectively.