Objective—To determine whether repetitive
sequence-based polymerase chain reaction (rep-PCR)
could be used to differentiate Streptococcus equi isolates,
to examine S equi isolates from throughout the
world, and to determine whether a horse had > 1 subtype
of S equi during an outbreak of disease.
Sample Population—An initial group of 32
S equi isolates, 63 S equi isolates from various geographic
areas, and 17 S equi isolates obtained during
outbreaks of disease.
Procedure—An aliquot of S equi genomic DNA was
amplified, using enterobacterial repetitive intergenic
consensus primers. Gel electrophoresis was performed
on 1.5% agarose gels, and a computed-assisted
program was used to compare rep-PCR results.
Results—Use of these primers to analyze 100 ng of
S equi genomic DNA resulted in patterns of 6 to 14
bands. The 32 initial isolates were separated into 7 rep-
PCR subtypes. There were 30 rep-PCR subtypes found
among 29 S equi isolates obtained from Minnesota,
Michigan, Canada, and Australia and 34 S equi isolates
obtained from Kentucky and other sources.
Furthermore, the same clone was identified in several
horses during an outbreak of disease. Infected horses
on the same farm all had a single clone of S equi.
Conclusion and Clinical Relevance—Analysis of
these results suggests that rep-PCR is useful for
delineating S equi into rep-PCR subtypes. Results
revealed that isolates with the same geographic
source or similar date of collection did not always
have the same rep-PCR subtype. A single clone of
S equi usually predominated during an outbreak of
disease. (Am J Vet Res 2000;61:699–705)