An investigation into the suitability of a commercial real-time PCR assay to screen for Taylorella equigenitalis in routine prebreeding equine genital swabs

Abstract

Reasons for performing study: Standard bacteriological methods for identifying Taylorella equigenitalis in cervical smears are time consuming. Therefore, a more rapid real-time PCR assay was evaluated for its suitability in screening swabs.

Objective: To compare the results of a commercially available real-time PCR assay with routine microbiological culture for the identification of T. equigenitalis, the causative organism of contagious equine metritis, in equine genital swab samples, under 'field trial' conditions.

Materials and methods: Routine prebreeding genital swabs (n=2072) collected from Thoroughbred mares and stallions during 2009 were examined together with stored T. equigenitalis positive material. Swabs were cultured for T. equigenitalis using standard microbiological techniques. Bacterial lysates were isolated from the swabs and examined for the presence of a 16S DNA fragment of T. equigenitalis, using a commercial multiplex real-time PCR assay system.

Results: There was complete concordance between positive and negative results obtained by the 2 methods. Real-time PCR also detected T. equigenitalis DNA from swabs that were negative using standard microbiological culture after 6 months' storage at +4 degrees C but from which T. equigenitalis had been isolated following collection. The sensitivities of real-time PCR and bacterial culture were both 10(-3) (equivalent to 3 colony-forming units).

Conclusion and clinical relevance: Routine bacterial culture of T. equigenitalis requires an incubation period of not less than 7 days before a conclusive negative result can be obtained, whereas bacterial extraction and real-time PCR assay can be completed in less than 6 h. The commercially-available PCR assay tested provided a rapid and reliable method for the identification of T. equigenitalis from equine genital swabs and could be usefully employed for the screening of mares and stallions for preseason Horserace Betting Levy Board (HBLB) Code of Practice and in other situations such as for bloodstock sales screening requirements, overcoming the current delays imposed by bacterial culture requirements. Its use could be quality assured by the existing HBLB biannual testing scheme for designated laboratories.