Streptococcal toxic shock syndrome caused by ST525 Streptococcus dysgalactiae subsp. equisimilis with genomic characterization of virulence and antimicrobial resistance.

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of severe invasive infections. We describe the clinical course of an immunocompromised patient with advanced breast cancer who developed streptococcal toxic shock syndrome, necrotizing fasciitis, and disseminated intramuscular abscesses caused by a multidrug-resistant Lancefield group G SDSE isolate, alongside a comprehensive genomic characterization of its virulence and antimicrobial resistance profiles. Genomic analysis identified the isolate as emm subtype stG840.0 and sequence type 525 (ST525), harboring genes encoding several virulence-associated factors, including an emm-like gene encoding an M-like surface protein, streptokinase, streptolysin O, streptolysin S, and SpeG. Through comprehensive genomic analysis of the highly virulent SDSE isolate, we provided insights into its underlying genetic background. Further accumulation of genomic data is expected to fully elucidate the mechanisms of virulence and antimicrobial resistance in SDSE.