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Rapid identification and fingerprinting of Candida krusei by PCR-based amplification of the species-specific repetitive polymorphic sequence CKRS-1

A PCR method was developed to identify and fingerprint Candida krusei isolates simply and rapidly. The primer pair Arno1 and Arno2 was designed to amplify the polymorphic species-specific repetitive sequence CKRS-1 (C. krusei repeated sequence 1) that we identified in the nontranscribed intergenic regions (IGRs) of rRNA genes in C. krusei LMCK31. The specificity, sensitivity, reproducibility, and fingerprinting ability of the PCR assay were evaluated. Amplification products were obtained from all 131 C. krusei isolates studied. No other yeast species of medical importance (n = 26), including species similar to C. krusei, species of pathogenic filamentous fungi, or a variety of pathogenic bacteria, yielded a PCR product with these primers. This PCR assay allowed for the identification of C. krusei in less than 6 h. The PCR assay was sensitive enough to detect as little as 10 to 100 fg of C. krusei-purified DNA and proved to be reproducible. Since amplification products varied both in number and in molecular weight according to the strains, PCR patterns allowed strains to be distinguished. To ascertain the epidemiological usefulness of this PCR fingerprinting, the patterns of the 131 isolates were compared. A total of 95 types which corresponded to 95 independent strains were delineated (discriminatory power = 1 with n = 95). Comparison of the results of PCR fingerprinting and those of fingerprinting with the CkF1,2 probe showed that they concurred. In addition, this work yields insights into the mechanisms involved in generating polymorphisms in the IGRs of C. krusei. Since this method is simpler and faster than established identification and genotyping methods of this important pathogenic species, it is a critical improvement for clinical microbiology laboratories relevant not only to diagnosis but also to epidemiology.