Persistence of Mycobacterium avium subsp. paratuberculosis at a Farm-Scale Biogas Plant Supplied with Manure from Paratuberculosis-Affected Dairy Cattle

Abstract

ABSTRACTIn this study, products from all steps of anaerobic digestion at a farm-scale biogas plant supplied with manure from paratuberculosis-affected dairy cattle were examined and quantified for the presence of the causal agent of paratuberculosis,Mycobacterium aviumsubsp.paratuberculosis, using culture and quantitative real-time PCR (qPCR). ViableM. aviumsubsp.paratuberculosiscells were detected using culture in fermentors for up to 2 months; the presence ofM. aviumsubsp.paratuberculosisDNA (101cells/g) was demonstrated in all anaerobic fermentors and digestate 16 months after initiation of work at a biogas plant, using IS900qPCR.F57qPCR was able to detectM. aviumsubsp.paratuberculosisDNA (102cells/g) at up to 12 months. According to these results, a fermentation process that extended beyond 2 months removed all viableM. aviumsubsp.paratuberculosiscells and therefore rendered its productM. aviumsubsp.paratuberculosisfree. However,M. aviumsubsp.paratuberculosisDNA was found during all the examined periods (more than 1 year), which could be explained by either residual DNA being released from dead cells or by the presence of viable cells whose amount was under the limit of cultivability. As the latter hypothesis cannot be excluded, the safety of the final products of digestion used for fertilization or animal bedding cannot be defined, and further investigation is necessary to confirm or refute this risk.