Mycobacterium tuberculosis remains a major cause of morbidity and mortality worldwide. Studies have reported human pathogens to have geographically structured population genetics, some of which have been linked to ancient human migrations. However, no study has addressed the potential evolutionary consequences of such longstanding human-pathogen associations. Here, we demonstrate that the global population structure of M. tuberculosis is defined by six phylogeographical lineages, each associated with specific, sympatric human populations. In an urban cosmopolitan environment, mycobacterial lineages were much more likely to spread in sympatric than in allopatric patient populations. Tuberculosis cases that did occur in allopatric hosts disproportionately involved high-risk individuals with impaired host resistance. These observations suggest that mycobacterial lineages are adapted to particular human populations. If confirmed, our findings have important implications for tuberculosis control and vaccine development.coevolution ͉ deletions ͉ lineage ͉ polymorphism ͉ population

Tuberculosis caused 20% of all human deaths in the Western world between the 17th and 19th centuries, and remains a cause of high mortality in developing countries. In analogy to other crowd diseases, the origin of human tuberculosis has been associated with the Neolithic Demographic Transition, but recent studies point to a much earlier origin. Here we used 259 whole-genome sequences to reconstruct the evolutionary history of the Mycobacterium tuberculosis complex (MTBC). Coalescent analyses indicate that MTBC emerged about 70 thousand years ago, accompanied migrations of anatomically modern humans out of Africa, and expanded as a consequence of increases in human population density during the Neolithic. This long co-evolutionary history is consistent with MTBC displaying characteristics indicative of adaptation to both low- and high host densities.

Drug-resistant bacteria are emerging worldwide, despite frequently being less fit than drug-susceptible strains1. Data from model systems suggest the fitness cost of antimicrobial resistance can be mitigated by compensatory mutations2. However, current evidence that compensatory evolution plays any significant role in the success of drug-resistant bacteria in human populations is weak3–6. Here we describe a set of novel compensatory mutations in the RNA polymerase of rifampicin-resistant Mycobacterium tuberculosis, the etiologic agent of human tuberculosis (TB). M. tuberculosis strains harbouring these compensatory mutations exhibited a high competitive fitness in vitro. Moreover, these mutations were associated with high in vivo fitness as determined by their relative clinical frequency across patient populations. Importantly, in countries with the world’s highest incidence of multidrug-resistant (MDR) TB7, more than 30% of MDR clinical isolates had such a mutation. Our findings support a role for compensatory evolution in the global epidemics of MDR-TB8.