Beta-hemolytic Streptococcus dysgalactiae strains isolated from horses are a
genetically distinct population within the Streptococcus dysgalactiae taxon
The pathogenic role of beta-hemolytic Streptococcus dysgalactiae in the equine
host is increasingly recognized. A collection of 108 Lancefield group C (n =
96) or L (n = 12) horse isolates recovered in the United States and in three
European countries presented multilocus sequence typing (MLST) alleles,
sequence types and emm types (only 56% of the isolates could be emm typed)
that were, with few exceptions, distinct from those previously found in human
Streptococcus dysgalactiae subsp. equisimilis. Characterization of a subset of
horse isolates by multilocus sequence analysis (MLSA) and 16S rRNA gene
sequence showed that most equine isolates could also be differentiated from S.
dysgalactiae strains from other animal species, supporting the existence of a
horse specific genomovar. Draft genome information confirms the
distinctiveness of the horse genomovar and indicates the presence of
potentially horse-specific virulence factors. While this genomovar represents
most of the isolates recovered from horses, a smaller MLST and MLSA defined
sub-population seems to be able to cause infections in horses, other animals
and humans, indicating that transmission between hosts of strains belonging to
this group may occur