Genetic heterogeneity of M type 3 group A streptococci causing severe infections in Tayside, Scotland.

To explain the worldwide increase in the frequency of severe infections by group A streptococci, molecular techniques are increasingly being employed to evaluate the genetic relationships of strains. We used restriction endonuclease analysis, pulsed-field gel electrophoresis (PFGE), the PCR, ribotyping, and DNA sequence analysis in a study of 13 group A streptococci isolated from a cluster of cases of serious infections over a 3-month period in Tayside, Scotland. Eight of the strains were M type 3; molecular characterization identified two subclones. The first, displaying PFGE profile 4, has been observed in Northern Scotland and has been circulating in New Zealand for over a decade. The second subclone has been documented only in the United Kingdom; it was first seen in 1993 in Scotland. Sequence analysis of emm-3 genes further differentiated the PFGE 4 subclone. DNA sequence analysis of virulence factors supports the suggestion that they may have recently been acquired by horizontal gene transfer.