P021 Comparative transcriptomic analysis of environmental Candida auris showing variable azole susceptibility

Abstract

Objective Candida auris is a multidrug-resistant pathogen that presents a serious global threat to human health. The U.S. Centers for Disease Control and Prevention has classified C. auris as an urgent threat to public health due to its clinical and economic impact and future projections of new infections over the next 10 years. Candida auris infections are difficult to treat since many isolates display high levels of resistance to fluconazole and exhibit variable resistance to amphotericin B and echinocandins. In this study, we performed comparative transcriptomics to understand the molecular mechanisms associated with azole-resistance in C. auris environmental isolates. Material and Methods: Two sets of environmental isolates including azole-resistant (n = 2) and azole susceptible (n = 1) isolates were used for RNA-Seq analysis. Pair-wise comparisons in edgeR were used for comparing the number of differentially expressed genes (DEGs) between the azole susceptible and resistant isolates. GO term enrichment analysis was performed using the ‘enrichGO’ function from the cluster Profiler package. Only GO categories with a q-value <0.05 were considered significant. Results Our data show significant enrichment of ergosterol biosynthesis genes, drug transport, MAPK pathway as well as chromatin remodeling genes in azole-resistant strains compared to susceptible isolates. A total of 468 and 564 differentially expressed genes were identified in two azole-resistant isolates compared with the susceptible strain. A large number of multidrug transporter genes (CDR1, MDR1, HGT2, HGT7, HGT13, HGT17, and NGT1) were differentially expressed between the two sets of strains. Interestingly, the overexpression of ERG11 (azole target gene), and CDR1 (drug transporter) genes was observed in resistant isolates as compared with susceptible strain. Furthermore, resistant strain has two copies of ERG11 while susceptible isolate has single copy of ERG11. Notably, 8/21 genes involved in the ergosterol biosynthesis pathway were found to be induced in azole resistant isolates. These include HMG1, ERG1, ERG2, ERG3, ERG6, ERG10, ERG13, and ERG25. Furthermore, other multidrug transporters MDR1 and SNQ2 responsible for azole resistance in other Candida species like C. glabrata also showed significant expression changes between the two sets of isolates. Furthermore, HGT7 (glucose transporter) and NGT1, (N-acetyl glucosamine transporter) genes associated with azole and polyene resistance were found to be upregulated in the resistant isolate as compared with susceptible strain. Additionally, a Glycophosphatidylinositol (GPI)-anchored protein unique for C. auris, PGA7 was found to be overexpressed in resistant isolate. Importantly, we also identified several secreted aspartic proteases (SAP3, SAP5, SAP8, and SAP9) to be downregulated between the two sets. Conclusion The present study identifies several gene families that are differentially expressed in azole resistant vs susceptible C. auris strains. These findings suggest that azole-resistance in C. auris environmental isolates is influenced by changes in cell wall, lipid, and ergosterol biosynthesis. Overall, these data provide a framework for the mechanistic understanding of azole resistance mechanisms in C. auris environmental isolates.