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. 2023 Nov 21;61(11):e0080623.
doi: 10.1128/jcm.00806-23. Epub 2023 Oct 25.

The first established microsatellite markers to distinguish Candida orthopsilosis isolates and detection of a nosocomial outbreak in China

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The first established microsatellite markers to distinguish Candida orthopsilosis isolates and detection of a nosocomial outbreak in China

Zhengyu Luo et al. J Clin Microbiol. .

Abstract

The infection proportion of Candida orthopsilosis, a member of the C. parapsilosis complex, has increased globally in recent years, and nosocomial outbreaks have been reported in several countries. This study aimed to establish microsatellite loci-based typing method that was able to effectively distinguish among C. orthopsilosis isolates. Three reference C. orthopsilosis genome sequences were analyzed to identify repeat loci. DNA sequences containing over eight bi- or more nucleotide repeats were selected. A total of 51 loci were initially identified, and locus-specific primers were designed and tested with 20 epidemiologically unrelated isolates. Four loci with excellent reproducibility, specificity, and resolution for molecular typing purposes were identified, and the combined discriminatory power (DP, based on 20 epidemiologically unrelated isolates) of these four loci was 1.0. Reproducibility was demonstrated by consistently testing three strains each in triplicate, and stability, demonstrated by testing 10 successive passages. Then, we collected 48 C. orthopsilosis non-duplicate clinical isolates from the China Hospital Invasive Fungal Surveillance Net study to compare the DP of the microsatellite-based typing with internal transcribed spacer (ITS) and amplified fragment length polymorphism (AFLP) typing analyses, using ATCC 96139 as a reference strain. These 49 isolates were subdivided into 12 microsatellite types (COMT1-12), six AFLP types, and three ITS types, while all the isolates with the same COMT belonged to consistent AFLP and ITS type, demonstrating the high DP of our microsatellite-type method. According to our results, COMT12 was found to be the predominant type in China, and COMT5 was the second largest and responsible for causing a nosocomial outbreak. This microsatellite-type method is a valuable tool for the differentiation of C. orthopsilosis and could be vital for epidemiological studies to determine strain relatedness and monitor transmission.

Keywords: AFLP; Candida orthopsilosis; microsatellite loci; microsatellite typing; outbreak.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig 1
Fig 1
AFLP analysis of 48 isolates and the reference strain ATCC 96139 and the corresponding relationships among AFLP, COMT, and ITS classification methods. The AFLP analyses results are presented on the left side of the graph, with the thin lines corresponding to AFLP types. The bold lines show the corresponding relationship between AFLP types and MT types, as well as MT types and ITS types. The colors of the bold lines only indicate different AFLP types.
Fig 2
Fig 2
The microsatellite types and clinical characteristics of 48 invasive C. orthopsilosis. (A) Minimum spanning tree analysis of 49 C. orthopsilosis based on allelic profiles at four microsatellite loci, and the shadow indicates the AFLP type. (B) Minimum spanning tree analysis of 49 C. orthopsilosis, and the colors represent different sample types. (C) Time axis of COMT12 type isolates. Strains are indicated as the hospital of isolation and the isolate number. (D) Number of strains isolated in hospitals H09 and H18 by year and month.

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