Genetic Relationships Deduced from <i>emm</i> and Multilocus Sequence Typing of Invasive <i>Streptococcus dysgalactiae</i> subsp. <i>equisimilis</i> and <i>S. canis</i> Recovered from Isolates Collected in the United States

<jats:title>ABSTRACT</jats:title> <jats:p> Beta-hemolytic group C and G streptococci cause a considerable invasive disease burden and sometimes cause disease outbreaks. Little is known about the critical epidemiologic parameter of genetic relatedness between isolates. We determined the <jats:italic>emm</jats:italic> types of 334 <jats:italic>Streptococcus dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> isolates, and attempted <jats:italic>emm</jats:italic> typing of 5 <jats:italic>Streptococcus canis</jats:italic> isolates from a recent population-based surveillance for invasive isolates. Thirty-four <jats:italic>emm</jats:italic> types were observed, including one from <jats:italic>S. canis</jats:italic> . We formulated multilocus sequence typing (MLST) primers with six of the seven loci corresponding to the <jats:italic>Streptococcus pyogenes</jats:italic> MLST scheme. We performed MLST with 65 of the 334 surveillance isolates (61 <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> isolates, 4 <jats:italic>S. canis</jats:italic> isolates) to represent each <jats:italic>emm</jats:italic> type identified, including 2 to 3 isolates for each of the 25 redundantly represented <jats:italic>emm</jats:italic> types. Forty-one MLST sequence types (STs) were observed. Isolates within 16 redundantly represented <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis emm</jats:italic> types shared identical or nearly identical STs, demonstrating concordance between the <jats:italic>emm</jats:italic> type and genetic relatedness. However, seven STs were each represented by two to four different <jats:italic>emm</jats:italic> types, and 7 of the 10 <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> eBURST groups represented up to six different <jats:italic>emm</jats:italic> types. Thus, <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> isolates were similar to <jats:italic>S. pyogenes</jats:italic> isolates, in that strains of the same <jats:italic>emm</jats:italic> type were often highly related, but they differed from <jats:italic>S. pyogenes</jats:italic> , in that <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> strains with identical or closely similar STs often exhibited multiple unrelated <jats:italic>emm</jats:italic> types. The phylogenetic relationships between <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> and <jats:italic>S. pyogenes</jats:italic> alleles revealed a history of interspecies recombination, with either species often serving as genetic donors. The four <jats:italic>S. canis</jats:italic> isolates shared highly homologous alleles but were unrelated clones without evidence of past recombination with <jats:italic>S. dysgalactiae</jats:italic> subsp. <jats:italic>equisimilis</jats:italic> or <jats:italic>S. pyogenes</jats:italic> . </jats:p>