Mycobacterium du jour: what's on tomorrow's menu?

Tremendous resources are being directed towards fundamental and applied research on Mycobacterium tuberculosis. Concurrently, diseases caused by other, non-tuberculous mycobacteria (NTM), are on the rise in many settings. For many of these 'atypical mycobacteria', there is no genome sequence data and a limited understanding of their biology. Consequently, they are often felt to be 'ubiquitous' in the environment and that disease occurs largely independent of bacterial factors, in an immunocompromised host. As the distribution of these organisms in human and environmental samples is decidedly non-random, there is indirect evidence that exposure, infection and disease due to these organisms are in part determined by bacterial factors. Knowledge on how different mycobacterial species engage the host differently will help provide predictive information on the epidemiology and biology of infection with these organisms. Already, post-genomic study of M. avium has pointed to the existence of variable genomic regions that likely represent mycobacterial pathogenicity islands. An additional benefit of further genomic study of NTM will be the provision of an out-group to better appreciate M. tuberculosis, potentially explaining the sequence of genomic events that originally permitted an environmental mycobacterium to evolve into a host-associated pathogen.