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 isolated in 1973 and before from patients with streptococcal pharyngitis, recent (1990s) serotype M3 clinical isolates from patients with pharyngitis, and recent M3 isolates from patients with toxic shock-like syndrome were investigated by restriction landmark genomic scanning and by modified random-amplified polymorphic DNA-polymerase chain reaction. Similar polymorphic DNA fragments were identified between the older M3 isolates and the recent isolates; also, the recent M3 clinical isolates from patients with pharyngitis were genetically indistinguishable, by the methods used, from the M3 isolates of patients with toxic shock-like syndrome. Although nucleotide sequences of these regions showed no apparent homology with known virulence factors, the DNA fragments could distinguish the recent M3 strains from the past strains. These results suggested that the recent strains have emerged because of genetic divergence.