Comparative genomics identifies a cyl-like region in Streptococcus sinensis isolates from a patient with infective endocarditis

Streptococcus sinensis is an uncommon member of the viridans group streptococci reported in infective endocarditis (IE), but its genomic characteristics remain incompletely defined. We performed whole-genome sequencing of three S. sinensis isolates recovered from blood culture and valvular tissue from a single patient with IE and compared them with 199 public Streptococcus genomes. Orthology analysis, phylogenetic reconstruction, SNP analysis, VFDB and CARD screening, gene-specific BLAST, Pfam/HMMER analysis, read mapping, synteny comparison, in silico structural modeling, and erythrocyte hemolysis assays were integrated. The three isolates differed by only 0–1 SNPs and formed a near-clonal group. Core single-copy ortholog phylogeny placed S. sinensis closest to S. cristatus , followed by S. sanguinis and S. gordonii . The three isolates retained the host-interaction-associated genes eno , pavA , and plr / gapA and carried an identical 11,341-bp, 12-gene cyl -like block comprising 11 cyl -like genes and acpC . Core-gene phylogeny analysis indicated that the distribution of the complete block was lineage-associated. Gene-specific BLAST and read mapping confirmed full-length sequence conservation and complete mapped-base coverage of the block, while Pfam/HMMER supported enzyme- and transporter-associated domain assignments for several encoded proteins. Structural modeling predicted soluble enzyme-like folds for CylG-like and CylZ-like proteins and a membrane-permease-like architecture with transmembrane helices for CylB-like. On Columbia sheep-blood agar, all three clinical isolates showed visible hemolytic zones and exhibited detectable hemolytic activity in a sheep erythrocyte hemolysis assay. All three S. sinensis isolates shared a type 1 CARD-derived resistance-marker profile containing only Spne_parC_FLO . These findings clarify the phylogenomic position of the near-clonal clinical isolates and identify a shared cyl -like genomic region accompanied by measurable hemolytic activity, providing a basis for further investigation of their host-interaction and pathogenic potential.