Mycobacterium avium subsp. paratuberculosis-specific mpt operon expressed in M. bovis BCG as vaccine candidate

Mycobacterium (M.) avium subspecies paratuberculosis is the etiological agent of paratuberculosis (Johne's disease) in ruminants. Vaccination against paratuberculosis with an attenuated live vaccine has been shown not only to prevent or reduce disease symptoms but also to have severe side effects. In contrast, the tuberculosis vaccine strain M. bovis BCG is considered safe and the efficacy of vaccination with M. bovis BCG transformants carrying foreign antigens has been shown in several studies. The mpt genes of M. avium subsp. paratuberculosis are part of a putative pathogenicity island and have been described as possible virulence determinants. In this study we show that the mpt genes are transcribed on a single polycistronic mRNA in M. avium subsp. paratuberculosis. We cloned the entire mpt operon, transformed it into M. bovis BCG Pasteur using the integrative vector pMV306 and showed transcription and expression of the mpt genes in the M. bovis BCG transformant. In a challenge experiment with Balb/c mice we demonstrated that immunization with M. bovis BCG expressing the M. avium subsp. paratuberculosis-derived mpt operon significantly reduces amplification of M. avium subsp. paratuberculosis in liver and spleen of the host in comparison to both the mock-immunized animals as well as the M. bovis BCG-immunized control. These findings imply that immunization with M. bovis BCG transformants may constitute a new strategy in the development of an efficacious and safe vaccine against paratuberculosis.