Recombinant 20.8-kDa protein of Mycobacterium avium subsp. paratuberculosis-based sero-diagnosis of paratuberculosis.

Johne's disease or paratuberculosis is a chronic infectious enteric disease of ruminants caused by the intracellular pathogen. The control of the Johne's disease is hampered by lack of specific diagnostic tests. In this study, we have cloned and expressed the N-terminal region of the locus tag Map 1637c encoding 20.8-kDa (r20.8) protein of Mycobacterium avium subsp. paratuberculosis. The recombinant protein r20.8 was expressed in high levels in Escherichia coli. The protein r20.8 was purified by single-step chromatography using Ni-NTA agarose. The protein r20.8 was reacted with anti-r20.8 antibodies as well as cattle sera infected with Map on Western blot. ELISA using well-characterized sera (both positive and negative; n = 60 each) Map-infected and non-infected cattle, respectively, yielded a sensitivity of 73.3% and a specificity of 98.3%. The 20.8 kDa protein expressed in the present study will prove useful as reagent in diagnostic test.