Multi-locus sequence typing of Candida tropicalis among Candiduria shows an outbreak in azole-susceptible isolates and clonal cluster enriched in azole-resistant isolates.

Background: The increasing detection rate of C. tropicalis and its azole resistance have made clinical treatment difficult. The presence of candiduria seems to correlate with invasive candida infection, especially for patients admitted to ICUs. However, the prevalence and antifungal resistance of C. tropicalis isolates in urine samples has not been well studied.

Aim: To retrospectively investigate the clinical features, antifungal resistance, and genetic relatedness of C. tropicalis isolates from urine samples.

Methods: A total of 107 clinical C. tropicalis isolates were retrospectively studied, including phenotypes of isolates and characteristics of patients. The genetic profiles of 107 isolates were genotyped using multi-locus sequence typing (MLST). Phylogenetic analysis was inferred using unweighted pair group method with arithmetic averages. MLST clonal clusters (CCs) were analysed by goeBURST.

Findings: Of the 107 isolates, 27.1% were resistant to fluconazole, and there was a notable increasing trend of fluconazole resistance from 16.1% in 2019 to 40.0% in 2021. Forty-seven diploid sequence types (DSTs) were assigned to ten major CCs. CC1 was the predominant fluconazole-susceptible group; 24 isolates from CC1 belonged to DST333, an outbreak clone in NICU ward. The azole-resistant CC4 contained 19 isolates, accounting for 65.5% of the azole-resistant isolates in this study. CC4 belongs to a prevalent FNS CC1 globally, of which the putative founder genotype was DST225.

Conclusion: This study revealed an outbreak of azole-susceptible C. tropicalis isolates in urine specimens and a high azole resistance rate of C. tropicalis in candiduria, and the MLST type showed clonal aggregation in azole-resistant isolates from urine samples.