Potential for residual contamination by Streptococcus equi subspp equi of endoscopes and twitches used in diagnosis of carriers of strangles.

This research examines the potential of endoscopes and twitches, tools used in veterinary practice specifically for horse treatment, to store and transmit Streptococcus equi subspp equi bacteria even after disinfection. The study tests the efficacy of different disinfectant methods and concludes that while most methods successfully remove the bacteria, residual DNA can remain on both types of tools.

Study Overview

• The study combined an experimental infection model and a field study to test the disinfection effects on endoscopes and twitches when exposed to standardized S equi bacterial solutions.
• The endoscope was disinfected using four different protocols involving various disinfectants for manual disinfection and an automated endoscope reprocessor (AER).
• For the twitches, 8 different disinfecting protocols were used.
• Lastly, endoscopes that were used in sampling for silent carriers were also disinfected following a field-based protocol. Each protocol was followed by tests for the presence of S equi, both in terms of live cultures and DNA remnants, using qPCR methods.

Results of the Study

• The results from the experimental contamination showed all endoscope disinfection protocols, apart from one-sixth of the ethanol protocol, resulted in a negative S equi culture.
• However, none of the endoscope disinfection protocols completely eliminated S equi DNA.
• In the case of the twitches, all were culture negative after the different disinfecting protocols had been followed. Out of all the disinfectants tested, only sodium hypochlorite completely eliminated detection of S equi DNA.
• The field disinfection of endoscopes that had been used for sampling silent carriers, yielded no culture positives, and all but one were qPCR negative.

Conclusion

• It is acknowledged that this laboratory model of experimental contamination may not accurately reflect the numbers of S equi transferred to endoscopes or twitches during their usage in the field, and that different secretions from infected horses may impact the bacteria’s survival rate.
• It is strongly suggested that while the majority of disinfection methods remove the live S equi bacteria, the tools can still host residual bacterial DNA.
• This finding signals a need for further investigation into the long-term impacts, if any, of this residual DNA and potential strategies for its complete removal.