Objectives: Rates of acquired resistance to triazoles and echinocandins are substantially higher among strains of Candida glabrata compared to other Candida species, particularly in the U.S. We previously demonstrated that disruption of the DNA mismatch repair (MMR) gene MSH2 increases C. glabrata antifungal resistance frequencies. Here, we feature the diversity of MSH2 polymorphisms identified in strains from around the globe and highlight their associated sequence types and relevance in resistance potential. Methods: We acquired over 900 strains of C. glabrata isolates from 10 U.S. states and 7 additional countries. Sequencing of drug target mutations (FKS1, FKS2, PDR1), MMR genes (e.g. MSH2), and multilocus sequence typing (MLST) is ongoing. Two cloning assays were developed to determine the significance of MSH2 polymorphisms. Results: Among U.S. isolates, we found that 94% (59/63) of fluconazole resistant isolates (MIC ≥ 32µg/ml) contained a PDR1 mutation and 90% (98/109) of echinocandin resistant isolates (MICs ≥ 0.25 µg/ml) contained an FKS1 and/or FKS2 mutation. Of these strains, 36 demonstrated multidrug resistance (both fluconazole and echinocandin resistance). MLST was performed on 68 of these resistant strains: ST10, ST16, ST8, ST3, and ST6 were the dominant (≥ 80%) STs. ST10, ST16, and ST8 are associated with Msh2 alleles carrying amino acid substitutions P208S/N890I, E231G/L269F, and V239L/A942T, respectively. These Msh2 alleles resulted in increased frequencies of drug resistant mutants when expressed in msh2Δ, indicating partial MMR loss of function (LOF). In 5 of 6 clinical isolates carrying partially deficient msh2 alleles, expression of pMSH2-WT caused a decrease in their resistant colony frequencies. ST3 and ST6 are Msh2-wild type (compared to CBS138/ATCC2001). Interestingly, ST10 and ST16 (and therefore their associated Msh2 alleles) are almost exclusively found within U.S. isolates. Other Msh2 alleles, primarily identified in international isolates, imparted partial (e.g. S346T, M651T) or no (e.g. E456D, E459K, R847C) Msh2 LOF. Greater genetic diversity in terms of MSH2 sequences and STs (including many novel STs) were identified within international isolates. Conclusions: Compared to the genetically diverse international isolate populations, C. glabrata from U.S. centers are enriched for several STs and, therefore, specific Msh2 alleles. It is possible that specific STs that have the ability to become more pathogenic or acquire drug resistance at greater rates have become more widespread within the U.S. Our data shed light on factors, such as MSH2, that may influence ST distribution.

Isolates of Candida glabrata from the United States are enriched for specific sequence types with distinct MSH2 alleles