نبذة مختصرة : Objectives: S. capitis is among the coagulase-negative staphylococci (CoNS) and a commensal bacterium in humans. However, a virulent clone designated NRCS-A has been reported to be responsible for outbreaks of neonatal sepsis, primarily in Europe. This clone harbors virulence factors nsr and tarJ, and carries a type V SCCmec, showing multiple antimicrobial resistance. This study explored the prevalence of the (proto-)NRCS-A clone in healthy individuals and their genetic characteristics in Japan. Methods: Staphylococci colonizing on the hand skin and the oral cavity of healthy individuals were isolated and analyzed for the species/subspecies by sequencing of 16S rRNA and arcC. The presence of virulence factors and antimicrobial resistance-associated genes were detected by PCR and sequencing. S. capitis isolates were genetically classified by double-locus (arcC-rpoB) sequence typing and peptide profile of PSMβ. Results: Among 221 isolates of CoNS (19 species) recovered from 444 healthy adults, 82 isolates were identified as S. capitis. Virulence factors associated with the NRCS-A clone, i.e., nsr, tarJ, and ebh were detected in 29 %, 11 %, and 51 % of isolates, respectively, while mecA/SCCmec V was positive in only one isolate harboring solely tarJ. arcC and rpoB were classified into 14 and 10 allelic types, respectively. PSMβ consisted of 3, 4, or 6 units of 44 amino acid-peptide, forming eight different profiles. Both virulence factors nsr and tarJ were detected in 5 isolates (6 %), among which two isolates had the same PSMβ profile and arcC-rpoB types as those of the NRCS-A clone prototype strain CR01. The mecA-positive isolate was classified into the same arcC-rpoB lineage as that of CR01. Conclusion: The present study revealed that SCCmec-negative S. capitis with nsr/tarJ (proto-NRCS-A clone) is distributed at low prevalence to healthy individuals in Japan. These isolates belonged to arcC-rpoB lineages close to that of the NRCS-A clone.
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