Microbiology of tubercle bacilli.

Based on conventional taxonomic analyses, as well as molecular level studies on DNA and catalases, the tuberculosis complex (M. tuberculosis, M. microti, M. bovis, and M. africanum) appears to consist of a single species. This species does not occur normally free in nature, but depends on host-to-host transmission for its continued existence. Members of the complex are sufficiently distinct genetically from known free-living mycobacteria so that it is unlikely that they would evolve from the free-living species at a significant frequency in nature, although that is presumably how they arose in the first place. Therefore, eradication of tuberculosis seems to be a realistic hope. The technical means now exist for control of the disease; some improvements in diagnostic technology can be expected to accelerate the control efforts. At a basic science level, more information is needed about the ability of M. tuberculosis to survive in a latent state in a host, only to revive years later, if the control of tuberculosis is to progress to eradication.