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

Background: C. tropicalis, its increasing detection rate and 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 was not well studied.

Objectives: Retrospectively investigate the clinical features, antifungal resistance and genetic relatedness of C. tropicalis isolates from urine samples.

Methods: 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 multilocus sequence typing(MLST). Phylogenetic analysis was inferred using unweighted pair group method with arithmetic averages (UPGMA). MLST clonal clusters (CCs) were analyzed by goeBURST.

Results: Of the 107 isolates, 27.1% were resistant to fluconazole, there was a notable increasing trend of fluconazole resistance from 16.1% in 2019 to 40.0% in 2021. 47 diploid sequence types (DSTs) were assigned to ten major CCs. CC1 was the predominant fluconazole-susceptible group, 24 isolates from CC1 were belonging to DST333, which was an outbreak clone in NICU ward. The azole-resistant CC4 contained 19 isolates, accounted for 65.5% of the azole-resistant isolates in this study. The CC4 belongs to a prevalent FNS CC1 globally, of which the putative founder genotype was DST225.

Conclusions: We firstly revealed an outbreak of azole-susceptible C. tropicalis isolates in urine specimen and a high azole resistant rate of C. tropicalis in candiduria, and the MLST type showed clonal aggregation in azole-resistant isolates from urine samples.