Streptococcus (S.) dysgalactiae subsp. equisimilis is responsible
for severe diseases in humans, including primary bacteraemia,
pneumonia, endocarditis, and toxic shock syndrome.
Infection in some animal species can also occur, although
a few studies have looked into cross-species infectivity. In
horses, S. equisimilis is generally considered infrequent or
opportunistic, but has recently been isolated from cases of
strangles-like disease. Rapid and sensitive diagnostic
techniques could enable epidemiological studies and effective
investigation of outbreaks involving these bacteria. In this
study, PCR protocols previously described in cattle and in
humans to detect the species S. dysgalactiae and the
subspecies equisimilis were evaluated to detect specific
sequences in equine samples. For this purpose, 99
monolateral nasal swabs were collected from horses from
stud farms with a history of S. equisimilis infection and
were tested blindly by bacteriological isolation and by
single and duplex PCR. DNA for PCR was extracted both
from the colonies grown on agar media and from
enrichment broth aliquots after incubation with nasal swab
samples. S. equisimilis was identified by bacteriological
isolation in 23 out of 99 swab samples, and PCR assays on
these colonies were fully concordant with bacteriological
identification (kappa statistic = 1.00). In addition, PCR of
the enrichment broth aliquots confirmed the bacteriological
results and detected S. equisimilis in 6 samples more than
the bacteriological examination (kappa statistic = 0.84). The
PCR protocols appeared to be reliable for the rapid
identification of S. equisimilis in equine nasal swab samples,
and could be useful for microbiological diagnosis.