Bulk tank milk samples from 392 Northern Ireland dairy farms, and individual milk from animals (n=293) on four of these farms, were tested by a novel phagomagnetic separation (PhMS)-qPCR assay in order to demonstrate its potential utility as a milk surveillance tool. Viable MAP were detected in 26.5% of the bulk tank milks, with MAP contamination levels ranging from 1-8432 MAP/50 ml milk; <2% of farms had MAP contamination levels >100 MAP/50 ml in their bulk tank milk. Follow up PhMS-qPCR testing of milk from individual animals on four farms that had the highest numbers of MAP in their bulk tank milks indicated the existence of 17-24% of animals in each herd shedding viable MAP in their milk. Mean MAP numbers detected ranged between 6.7 and 42.1 MAP/50 ml milk. No significant correlation was observed between detection of viable MAP in bulk or individual milks by PhMS-qPCR and parallel milk-ELISA result, or indeed between PhMS-qPCR results and any other milk recording parameter (somatic cell count, total bacterial count (Bactoscan), butterfat % or protein %). A second 50 ml aliquot of 61 PhMS-qPCR positive individual milk samples from the four farms was cultured in MH7+ (Pozzato) broth following peptide-mediated magnetic separation. Fifty-two (85.2%) broth cultures showed evidence of MAP by IS900 qPCR after incubation, thereby confirming that a PhMS-qPCR positive result was generally a true indication of the presence of viable MAP in the milk sample. Our findings clearly demonstrate that the novel PhMS-qPCR assay could be a useful milk surveillance tool for dairy processors, or a milk monitoring tool for Johne’s disease control or milk quality assurance programs.
|Journal||Journal of Dairy Science (Official journal of the American Dairy Science Association)|
|Publication status||Accepted - 30 Dec 2020|
- Cows' milk
- Johne's disease
- Mycobacterium avium subsp. paratuberculosis (MAP)
- Phagomagnetic separation
- Quantitative PCR