Enhanced detection of Taylorella equigenitalis by qPCR using 'Dry' swabs

Abstract

Detection of Taylorella equigenitalis (CEMO) in the horse uses genital swabs. These swabs traditionally have been put in Amies charcoal transport medium for detection by culture but are also used for PCR. We determined the suitability of swabs without transport medium (Dry swabs) for CEMO PCR compared to swabs in Amies charcoal transport medium. The experiment was a factorial design using swab type and dilution of organism in culture suspensions, done in two parts. Simulated genital swabs were prepared in the laboratory by dipping in pairs into culture suspensions containing T. equigenitalis with or without other organisms, and then inserting them into a sleeve either with or without transport medium. In study 1, the difference in Ct value for the two swab types was compared. In study 2 genital swab material was then also added to culture suspensions and the swab types again compared. The swabs were tested by a validated quantitative PCR method. The Ct value of the PCR test was used as the measure for comparison, and the effect of variables assessed with linear regression. There was an 7.7% (6.5-8.9) higher mean Ct value of TM versus Dry swabs (P<0.001) overall. The Ct difference was more marked at higher dilutions. Addition of genital swab material had no effect on the Ct value. Dry swabs perform at least as well for PCR as swabs in Amies charcoal transport medium, especially when relatively low numbers of organism are present, and are advantageous for routine sampling when culture is not being used.

Keywords: Amies charcoal transport medium; contagious equine metritis; diagnosis; genital.

Fig. 1.

Ct values (untransformed) for individual Dry and TM simulated CEM-swabs from each of the two study parts and, for illustrative purposes, fitted lines over the log10 dilution. Only 3 dilutions were used in the second study. Pairing is not shown.

Fig. 2.

Ct values (untransformed) for individual samples and, for illustrative purposes, fitted lines for ‘pure’ and ‘field’ (containing genital swab material) simulated CEM-swabs in study 2. Dry and TM swabs are not differentiated.