Interspecies Recombination Occurs Frequently in Quinolone Resistance-Determining Regions of Clinical Isolates of Streptococcus pyogenes

The phylogenetic tree is based on the parC QRDR sequences, was constructed with the MrBayes program (version 3.0B4), and was rooted with Streptococcus canis as the outgroup. All Streptococcus pyogenes sequences are designated with their respective GenBank identifiers. Susceptibility to fluoroquinolones is indicated in parentheses, as follows: R, resistant; S, susceptible; ?, not found in the literature. Horizontal gene transfer between Streptococcus pyogenes GAS14 and Streptococcus dysgalactiae subsp. dysgalactiae is strongly suggested by the small distance and the highest possible posterior probability of the branching (posterior probability, 1.0).