Survival of Mycobacterium avium ssp. paratuberculosis in yoghurt and in commercial fermented milk products containing probiotic cultures

Abstract

To assess the survival of Mycobacterium avium ssp. paratuberculosis (MAP) in yoghurt and commercial fermented milk products containing probiotic strains. Whole and skimmed UHT milk artificially inoculated with MAP were used to manufacture yoghurt, using two different yoghurt starter cultures. Five commercial fermented milk products were inoculated with MAP. Two different MAP strains were studied. The survival of MAP in all products was monitored by culture over a 6-week storage period at 6°C. In yoghurt, MAP counts did not change appreciably during the storage period. Fat content and type of yoghurt starter culture had no consistent effect on the survival of MAP. In the fermented milk products, survival patterns varied but resulted in a 1·5 to ≥3·8 log reduction for the Niebüll strain and a 1·2-2·2 log reduction for the NIZO strain after 6 weeks, depending on the probiotic starters present in the product. MAP easily survived in yoghurt but MAP numbers decreased in fermented milk products containing probiotic cultures. The results contribute to the lack of knowledge on the behaviour of MAP in yoghurt and fermented milk products containing probiotic cultures. This knowledge is valuable in the context of the risk of MAP transmission to humans via yoghurt and the possible contribution of probiotic fermented milk products to the elimination of MAP.