Genotyping of Candida tropicalis isolates uncovers nosocomial transmission of two lineages in Italian tertiary care hospital.

OBJECTIVES: Candida tropicalis is a medically important yeast with increasing antifungal resistance, but nosocomial transmission is rarely reported. This study genotyped C. tropicalis isolates from Italian hospitals to uncover potential nosocomial transmission and assess resistance.

METHODS: In total, 197 C. tropicalis isolates from 161 patients were collected from five centres from 2013 to 2023. Short tandem repeat (STR) genotyping was conducted on all isolates, and a selection of 24 isolates were typed with whole-genome sequencing (WGS) and the novel Fourier-transform infrared (FTIR) spectroscopy method. Antifungal resistance was investigated with microbroth dilution and WGS.

RESULTS: STR genotyping revealed seven clusters with isolates from multiple patients. WGS single nucleotide polymorphism (SNP) analysis on five groups of isolates with related STR genotypes also separated these isolates into five groups, of which two groups contained a cluster of isolates from different patients distinguished by ≤59 SNPs. In comparison, sequential isolates within three patients were differentiated by ≤141 SNPs. The two C. tropicalis WGS clusters also clustered based on FTIR genotyping, although this method did not separate the isolates into five groups. None of the 24 isolates were resistant to common antifungals.

CONCLUSIONS: WGS SNP analysis indicated nosocomial transmission of two lineages within the same hospital, highlighting the need for enforced infection prevention measures and routine genotyping on this common yeast in clinical settings. While both STR and FTIR genotyping also clustered these lineages, WGS SNP analysis is required to determine whether isolates were transmitted clonally.