Analysis of fks1 and fks2 gene mutations in invasive Candida glabrata strains from Pakistan.

Introduction: The gradual increase in caspofungin usage in Pakistan raises a concern of emergence of echinocandin resistance in local Candida glabrata strains. We sequenced and determined mutations in fks1 and fks2 genes in invasive Candida glabrata strains from Pakistan.

Material And Methods: Thirty-six invasive C. glabrata strains were selected with median (min-max) minimum inhibitory concentrations (MICs) of 0.06 (0.015-0.25) mg/L for caspofungin, 0.015 (0.008-0.06) mg/L for micafungin and 0.06 (0.015-0.12) mg/L for anidulafungin. fks1 and fks2 gene fragments were sequenced using Sanger methodology. Sequences were analysed with MEGA-6 software to identify specific single-nucleotide polymorphisms (SNP) against wild-type sequences of C. glabrata.

Results: In fks1 gene, non-synonymous mutation D632H was observed in one isolate with caspofungin MIC of 0.25 mg/L. Synonymous mutation at position A742 was observed in 26/36 (72%) of the isolates. 34/36 (94.5%) isolates analysed for fks2 gene were observed as wild type. A novel non-synonymous mutation at I661T was observed in fks2 gene in one isolate with caspofungin MIC of 0.12 mg/L and anidulafungin and micafungin MIC of 0.06 and 0.015 mg/L, respectively. Novel fks2 synonymous mutations at position T647, K652 and I706 were observed in 16/36 (44%), 25/36 (69%) and 23/36 (63%) isolates, respectively.

Conclusion: Low frequencies of both non-synonymous and synonymous polymorphisms were observed in invasive C. glabrata strains. Since S663P in fks2 gene is associated with caspofungin resistance, a novel mutation at 661 codon identified in our study needs correlation with treatment outcome data and mandates periodic genomic surveillance.