Submitted to: Journal of Medical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2001
Publication Date: N/A
Interpretive Summary: Mycobacterium paratuberculosis is a pathogen of cattle and sheep that causes Johne's disease. While the animal may die from this ailment, the disease is more economically devastating to the animal producers resulting in 100 million dollar loses annually. Very little is known about how Mycobacterium paratuberculosis causes disease. It is known that the macrophage is the predominant host cell that M. paratuberculosis grows and survives within. Therefore, by understanding what genes M. paratuberculosis expresses within the macrophage may help us to understand how it can grow and survive there. Armed with this increased understanding we can begin to design strategies that will cripple growth within the macrophage which may eventually cure the disease. In this report, we identified two genes that were detected only when live, not killed, M. paratuberculosis was present in a rabbit host. One of these genes was shown to be present within M. paratuberculosis macrophages. This finding is exciting because, to our knowledge, it is the first such M. paratuberculosis protein to be detected within the macrophage. Further study will determine if this protein is directly involved in enabling growth within macrophages.
Technical Abstract: The investigation of environmentally regulated proteins have led to a better understanding of host-pathogen interactions and have identified novel vaccine candidate antigens for several bacterial pathogens. In an effort to identify such proteins in Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis), a genomic expression library was differentially screened with sera from rabbits that had been immunized with live M. paratuberculosis (a-live) as well as sera from rabbits immunized with heat-killed M. paratuberculosis (a-killed). These experiments identified seven recombinant plaques that are uniquely recognized by the a-live sera. Sequence data showed that five of these clones overlapped with each other and contained a common open reading frame encoding a 25-kDa protein, termed Csp1. The 25-kDa antigen shows weak similarity to a secreted Corynebacterium glutamicum protein. The remaining two clones overlapped with each other and contained two partial open reading frames, both encoding proteins with strong homology to polyketide synthase from various species of mycobacteria. Antisera were produced against a peptide of the polyketide synthase gene product designated Pks7. Csp1-specific antibodies were affinity purified from the a-live sera. These purified antibodies demonstrated that Csp1 was present within infected macrophages. Collectively, these data identify novel paratuberculosis antigens that may be important in pathogenesis.