A predominant genotype of azole-resistant Candida tropicalis clinical strains

Through the Taiwan Surveillance of Antimicrobial Resistance of Yeasts (known as TSARY), we found that Candida tropicalis was not the most common non-albicans Candida species, but C tropicalis does have a higher fluconazole-resistant rate than other Candida species. We detected that 45·3% (24/53) of fluconazole-non-susceptible C tropicalis collected in 1999 and 2006 belonged to the same cluster: clade 5; according to the multi-locus sequence typing method. We found that 9·2% (56/608) of C tropicalis from 2014 and 2018 were resistant to fluconazole. 94·6% (53/56) of fluconazole-resistant C tropicalis were genetically closely related and belonged to clade 4, rather than clade 5. A combination of mutation and overexpression of ERG11 was the major mechanism that contributed to the drug resistance of clade 4.1Zhou ZL Tseng KY Chen YZ et al.Genetic relatedness among azole-resistant Candida tropicalis clinical strains in Taiwan from 2014 to 2018.Int J Antimicrob Agents. 2022; 59e106592Crossref Scopus (0) Google Scholar Multi-locus sequence typing is a convenient and cost-effective tool for studying the genetic relatedness and genetic diversity of isolates. Nevertheless, the method might have some limitations as it evaluates DNA fragments of maximum six genes only. In the present study, to assess the data from multi-locus sequence typing, we compared the mitochondrial genome sequence of 34 tested clinical isolates. Despite different drug susceptibilities, the genetic relatedness of the two clusters as identified by multi-locus sequencing, was confirmed by the mitochondrial genome sequence (appendix). Hence, multi-locus sequencing is still a viable approach for rapidly identifying the genetic relatedness among C tropicalis isolates. Our preliminary data showed that 87·0% (40/46) of fluconazole-susceptible clade 5 isolates had high fluconazole minimum inhibtory concentrations after longer incubation. Therefore, the clade 5 isolates could survive in the presence of low levels of fluconazole and might be prone to fluconazole resistance. An outbreak of Candida auris in a neuroscientific intensive care unit in the UK was linked to reusable axillary temperature probes.2Eyre DW Sheppard AE Madder H et al.A Candida auris outbreak and its control in an intensive care setting.N Engl J Med. 2018; 379: 1322-1331Crossref PubMed Scopus (220) Google Scholar Among 21 C tropicalis isolates from patients in Italy, nine belonged to the genotype DST747 and six belonged to DST333. Isolates from hospital environments and the hands of health-care workers also belonged to either of these two DST genotypes.3Scordino F Giuffre L Barberi G et al.Multilocus sequence typing reveals a new cluster of closely related Candida tropicalis genotypes in Italian patients with neurological disorders.Front Microbiol. 2018; 9: 679Crossref PubMed Scopus (13) Google Scholar Therefore, a specific Candida species clone can persist in the environment and be horizontally transmitted within a health-care setting. In addition to our findings, 23 of the 30 (76·7%) fluconazole-resistant C tropicalis from China belonged to clade 4.4Wang Y Shi C Liu JY Li WJ Zhao Y Xiang MJ Multilocus sequence typing of Candida tropicalis shows clonal cluster enrichment in azole-resistant isolates from patients in Shanghai, China.Infect Genet Evol. 2016; 44: 418-424Crossref PubMed Scopus (15) Google Scholar Hence, active surveillance to detect the emergence and dissemination of azole-resistant C tropicalis in clinical, hospital, and community environments might help us to elucidate how these resistant isolates spread in the wild and how they persist, which could help to prevent further spread of clade 4. This work was supported by research grants from the National Health Research Institutes, Taiwan (grant numbers: IV-110-PP-03; IV-110-SP-03; IV-111-PP-10; IV-111-SP-01); from the Taiwan Centers for Disease Control (grant number: 10D9-IVICDC02); and from Taiwan's Ministry of Science and Technology (grant number: 110-2314-B-400-040). All authors declare no competing interests. We thank Yin-Zhi Chen and Hugo Evers (National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli County, Taiwan), and Mark Swofford (Scientific Editing Office, National Health Research Institutes, Miaoli County, Taiwan). Download .pdf (1.64 MB) Help with pdf files Supplementary appendix