Controlling the spread of Johne’s disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP), in domestic livestock is challenging. Current diagnostic methods lack sufficient sensitivity to detect sub-clinically infected animals, and thus better diagnostic methods are needed. This study was carried out to investigate the diagnostic potential of two novel peptide-mediated magnetic separation (PMS)-based tests - a PMS-phage assay and PMS-culture – both of which have been developed and optimised to detect viable MAP cells in bovine milk. Individual milk samples (50 ml) were obtained from 105 ‘non-infected’ and 40 ‘MAP-infected’ animals (classified as such on the basis of prior faecal culture and serum-ELISA results) in three dairy herds, and tested in parallel by the PMS-phage assay and PMS-culture. Diagnostic sensitivity (DSe) and specificity (DSp) of the PMS-phage and PMS-culture methods were determined relative to the MAP infection status of the animal contributing the milk sample. The PMS-based tests applied individually showed moderate DSe (PMS-culture 0.250 and PMS-phage assay 0.325) and high DSp (0.962 and 1.000, respectively). When results of the two PMS-based tests were combined, DSe increased substantially to 0.525 and the DSp was calculated to be 0.962. It was concluded that combined application of the PMS-phage assay and PMS-culture provided the most complete picture regarding the presence of viable MAP in bovine milk samples. A comprehensive validation of the PMS-based assays relative to currently used diagnostic methods (faecal culture and serum-ELISA) would be the next step in assessment of the diagnostic potential of these novel PMS-based methods.
- Mycobacterium avium subsp. paratuberculosis
- Diagnostic Techniques and Procedures
- Peptide-mediated magnetic separation (PMS)
- Milk testing
- Johne's disease
- PMS-phage assay