Genetic diversity and virulence of group isolates from bloodstream infections.

catheter-related bloodstream infections (CRBSIs) are an increasing concern in Japanese hospitals. Although their clinical characteristics have been explored, the genetic relationships and virulence profiles of isolates from CRBSIs remain understudied. Here, using advanced genomic techniques, we investigated the genetic diversity, phylogenetic relationships, and virulence profiles of isolates from patients with bloodstream infections. We analyzed 28 group strains isolated from blood samples at the University of Tokyo Hospital between 2005 and 2017 using whole-genome sequencing, core-genome single-nucleotide polymorphism (SNP) typing, and virulence gene profiling. Core-genome SNP analysis revealed significant genetic diversity among the isolates, suggesting multiple independent sources of infection. The isolates predominantly belonged to clades III and IV, with distinct virulence gene profiles. All clade III isolates contained operon genes, whereas four isolates from clade IV harbored cereulide synthetase genes (). One isolate possessed a capsule gene operon (), a rare finding among clinical strains. Biofilm formation ability was observed in 50% of catheter-related isolates, although this ability was not significantly different from that of the noncatheter-related isolates.IMPORTANCEThis study provides novel insights into the genetic diversity and virulence potential of strains causing bloodstream infections in a Japanese hospital setting. These findings suggest diverse infection pathways and highlight the importance of continuous molecular epidemiological surveillance for effective infection control.