Optimization of an in vitro assay to detect Streptococcus equi subsp. equi.

The research article focuses on optimizing an in vitro testing method to detect Streptococcus equi, a bacteria causing upper respiratory illness in horses. The scientists propose and test different methods to improve the sensitivity and accuracy of the detection.

Introduction and Hypothesis

• The research is centered around Streptococcus equi, a bacterium causing ‘strangles’, a major respiratory infection in horses.
• Although bacterial culture methods and PCR (Polymerase Chain Reaction) of nasopharyngeal washing and guttural pouch lavages are used conventionally to detect the bacteria, an optimal detection method remains undetermined.
• The scientists hypothesize that using a flocked swab soaked in serially diluted suspensions of the bacteria will detect more colony-forming units (CFUs) than a rayon swab.
• The researchers also believe that centrifuging a part of each suspension will improve the limit of detection (LOD) for bacterial culture and PCR compared to submerged swab samples.
• The assumption is also made that PCR of centrifuged samples will be more sensitive than aerobic culture alone.
• It’s also proposed that PCR of a direct sample would be more sensitive than one following the submersion of a swab in saline.

Methodology and Results

• Seven ten-fold serial dilutions of S. equi in 0.9% NaCl was used, and LOD for 4 bacterial culture methods and 3 PCR methods were compared.
• The research found that the LOD was the same for both direct PCR and flocked swab culture, at 1 cfu/ml.
• All PCR methods were found to be equivalent in sensitivity and more sensitive than any of the culture methods for lower dilutions.
• However, at higher cell densities (more than 100 cfu/ml), the flocked swab culture method was not statistically more effective than rayon swab culture, but it was notably superior to all other methods tested.

Conclusion

• This article suggests new considerations for optimal methods to detect and assess the S. equi bacterial concentration in test samples. Gaining more accurate readings at various dilutions is crucial to managing this common equine disease.
• The results give a valuable insight into the effectiveness of different testing methods and offer a springboard for further research into this area.