RESUMEN
AIMS: To assess the survival of Mycobacterium avium ssp. paratuberculosis (MAP) in yoghurt and commercial fermented milk products containing probiotic strains. METHODS AND RESULTS: 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. CONCLUSIONS: MAP easily survived in yoghurt but MAP numbers decreased in fermented milk products containing probiotic cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: 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.
Asunto(s)
Productos Lácteos Cultivados/microbiología , Microbiología de Alimentos , Mycobacterium avium subsp. paratuberculosis/crecimiento & desarrollo , Probióticos , Yogur/microbiología , Animales , Bifidobacterium/crecimiento & desarrollo , Recuento de Colonia Microbiana , Fermentación , Manipulación de Alimentos , Lactobacillus/crecimiento & desarrollo , Viabilidad Microbiana , RefrigeraciónRESUMEN
The purpose of the study was to determine the distribution of Mycobacterium avium ssp. paratuberculosis (MAP) across the main milk and colostrum fractions (cream, curd, and whey). Raw milk and colostrum were inoculated with 1 of 2 MAP strains, ATCC 19698 or S-23, yielding initial concentrations of 10(6) to 10(7) cfu/mL. After fractionation, for milk as well as for colostrum, 80 to 90% of the recovered MAP cells were found in the curd fraction and 10 to 20% in the cream fraction. Total MAP colony counts in milk whey were 4 to 5 log(10) units lower than colony counts of inoculated milk. In colostrum, colony counts were 2 to 3 log(10) units lower in whey than in inoculated colostrum. Because of the slow growth of MAP and to proceed more smoothly with set-up and optimization of the method, luminescent MAP strains were used. The high correlation coefficient (r=0.960) between colony counts and luminescence measurements showed that the use of luminescent MAP strains during method development was plausible.