A novel invasive Streptococcus pyogenes variant sublineage derived through recombinational replacement of the emm12 genomic region.

Group A streptococcal strains potentially acquire new M protein gene types through genetic recombination (emm switching). To detect such variants, we screened 12,596 invasive GAS genomes for strains of differing emm types that shared the same multilocus sequence type (ST). Through this screening we detected a variant consisting of 16 serum opacity factor (SOF)-positive, emm pattern E, emm82 isolates that were ST36, previously only associated with SOF-negative, emm pattern A, emm12. The 16 emm82/ST36 isolates were closely interrelated (pairwise SNP distance of 0-43), and shared the same emm82-containing recombinational fragment. emm82/ST36 isolates carried the sof12 structural gene, however the sof12 indel characteristic of emm12 strains was corrected to confer the SOF-positive phenotype. Five independent emm82/ST36 invasive case isolates comprised two sets of genetically indistinguishable strains. The emm82/ST36 isolates were primarily macrolide resistant (12/16 isolates), displayed at least 4 different core genomic arrangements, and carried 11 different combinations of virulence and resistance determinants. Phylogenetic analysis revealed that emm82/ST36 was within a minor (non-clade 1) portion of ST36 that featured almost all ST36 antibiotic resistance. This work documents emergence of a rapidly diversifying variant that is the first confirmed example of an emm pattern A strain switched to a pattern E strain.