676 - New PLST Locus for Sequence-based Typing of Candida glabrata Clinical Isolates

Background: Healthcare-associated infections (HAI) with the opportunistic yeast Candida glabrata have become increasingly common in the fluconazole era, and may be endogenous or nosocomial in origin. Effective intervention requires distinguishing between these sources, which in turn requires epidemiological analysis in conjunction with isolate typing. Multiple approaches to C. glabrata typing have been described, ranging from length-based microsatellite and PFGE analyses to sequence-based MLST and WGS; however, issues of cost and technical complexity preclude their routine use in clinical labs. Polymorphic locus sequence typing (PLST) addresses these issues by employing conventional PCR and Sanger sequencing of selected tandem repeat loci that exhibit high rates of both SNPs and insertion/deletion. In our previous study, PLST loci CgMT-J and CgMT-M resolved 104 isolates into 10 phylogenetic clusters and 20 to 24 alleles (Katiyar et al., 2016, J. Clin. Microbiol. 54:1042). Within clusters N and P, isolates from 4 patients each (sets DSY and KM) who received treatment at the same healthcare facilities shared alleles. While consistent with nosocomial transmission, these alleles were also shared by epidemiologically unrelated strains.

Methods: CgMT-J/CgMT-M were identified by bioinformatic analysis of the only two, closely related C. glabrata genome sequences available at the time. Since current GenBank databases include sequences for 16 strains, including 4 epidemiologically related pairs, we bioinformatically searched for new loci exhibiting greater strain resolution.

Results: Locus CgMT-C represents an intergenic region on chromosome C that includes multiple tandem repeats and has no detectable homolog in other yeast. Phylogenetic analysis of database sequences resolved all 12 unrelated strains. In the laboratory, the CgMT-C locus was readily amplified and sequenced directly from C. glabrata colony lysates, including those prepared from chromogenic agars. Most importantly, CgMT-C analysis confirmed identities of the cluster N and P isolates from DSY and KM patients, and resolved them from all unrelated strains.

Conclusion: CgMT-C PLST represents a powerful new tool for C. glabrata epidemiology and infection control.