Genetic Profiling of Four Drug Resistant, Biofilm Forming Clinical Isolates of Candida tropicalis

Candida tropicalis is a prominent non-Candida albicans Candida (NCAC) species that causes superficial as well as life-threatening infections and common cause of nosocomial infections in India. Understanding C. tropicalis drug resistance is of great importance because of the recalcitrant strains of C. tropicalis causing long term and persistent infections and hyper inflammation. The aim of this study was to understand the genetic basis of etiology of the locally obtained clinical isolates of C. tropicalis and to study the evolutionary changes of genes involved in biofilm formation, antifungal resistance, and viability. In this study, biofilm formation by the clinical isolates of C. tropicalis was estimated through semi-quantitative assays and drug resistance was determined. These isolates were fluconazole resistant but were inhibited by aqueous extracts of garlic. Four isolates C4, U873, U1179 and U1360 of C. tropicalis with relatively high and low biofilm formation were considered for Whole Genome Sequencing. The identification of the functional effects of SNPs and InDels in the isolates showed that the relatively high biofilm forming ability was due to two genes CTRG_06254 an alpha 1-6 mannosyl transferase and CTRG_02593 a fungal zinc cluster transcription factor, important in biofilm formation and drug resistance respectively. In the relatively high biofilm forming isolates, there were lower numbers of missense variant effects whereas in the relatively low biofilm forming isolates, the agglutinin-like protein orthologs were observed to have higher number of missense effects. From the MLST analysis, three novel alleles were observed in the loci of MDR1 and XYR1 genes. The evolutionary lineage of the clinical isolates was also studied. The identification of C. tropicalis isolates was optimized by PCR based detection method. This study overall reveals the evolutionary changes in the genomes of locally relevant clinical isolates of C. tropicalis.