Genomic differences in Streptococcus pyogenes serotype M3 between recent isolates associated with toxic shock-like syndrome and past clinical isolates

Genomic differences among past Streptococcus pyogenes serotype M3 strains i solated in 1973 and before from patients with streptococcal pharyngitis, re cent (1990s) serotype M3 clinical isolates from patients with pharyngitis, and recent M3 isolates from patients with toxic shock-like syndrome were in vestigated by restriction landmark genomic scanning and by modified random- amplified polymorphic DNA-polymerase chain reaction. Similar polymorphic DN A fragments were identified between the older M3 isolates and the recent is olates; also, the recent M3 clinical isolates from patients with pharyngiti s were genetically indistinguishable, by the methods used, from the M3 isol ates of patients with toxic shock-like syndrome. Although nucleotide sequen ces of these regions showed no apparent homology with known virulence facto rs, the DNA fragments could distinguish the recent M3 strains from the past strains. These results suggested that the recent strains have emerged beca use of genetic divergence.