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Optimization of an in vitro assay to detect Streptococcus equi subsp. equi
Ashley G Boyle1, Ray C Boston, Kathleen O'Shea
1Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, 382 West Street Rd., Kennett Square, PA 19348, USA. boylea@vet.upenn.edu
Veterinary Microbiology
|May 8, 2012
Summary
Flocked swabs and PCR offer improved detection of Streptococcus equi, the cause of strangles in horses. PCR methods are more sensitive than bacterial culture, especially at low bacterial concentrations.
Area of Science:
- Veterinary Microbiology
- Equine Infectious Diseases
- Diagnostic Microbiology
Background:
- Strangles, a highly infectious equine respiratory disease, is caused by Streptococcus equi.
- Current diagnostic methods for S. equi, including bacterial culture and PCR of nasopharyngeal samples, lack a definitive optimal test.
Purpose of the Study:
- To compare the efficacy of flocked swabs versus rayon swabs for S. equi detection.
- To evaluate the impact of sample centrifugation on bacterial culture and PCR sensitivity.
- To determine the optimal diagnostic method for S. equi detection in horses.
Main Methods:
- Ten-fold serial dilutions of S. equi were prepared and inoculated using flocked and rayon swabs.
- Bacterial culture and PCR were performed on swab samples and centrifuged aliquots.
- Limit of detection (LOD) was determined for various culture and PCR methods.
Main Results:
- The limit of detection for direct PCR and flocked swab culture was 1 CFU/ml.
- All PCR methods demonstrated higher sensitivity than bacterial culture at lower S. equi dilutions.
- At higher bacterial densities (>100 CFU/ml), flocked swab culture showed no statistical advantage over rayon swab culture but outperformed other methods.
Conclusions:
- PCR-based methods are more sensitive than traditional culture for detecting low levels of S. equi.
- Flocked swabs offer advantages in bacterial culture sensitivity, particularly for low bacterial loads.
- Further optimization of diagnostic techniques is needed for definitive S. equi detection in equine strangles.
