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)