We have used molecular techniques to characterize 51 group A streptococci from Scotland and 17 ‘serious disease’ isolates from other countries, in order to establish the clonal structure of invasive Streptococcus pyogenes strains circulating between 1986 and 1993. Strains were grouped by restriction endonuclease analysis, pulsed field gel electrophoresis and ribotyping patterns, and were examined for the presence of alleles of the speA gene by polymerase chain reaction and DNA sequence analysis. Serious and fatal infections in Scotland were caused by several clones. One clone (9 of 51 strains) was M type 1 and possessed the speA gene allele 2. This was the clone previously identified as causing severe infection in the USA. Another clone (5 of 51 strains) was M type 3 and had speA gene allele 3. In view of the clear association of more than one clone with severe, invasive and fatal infections, horizontal gene exchange between genotypes merits further investigation.
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