Origin, Spread and Demography of the Mycobacterium tuberculosis Complex

TLDR

The evolutionary timing and spread of the Mycobacterium tuberculosis complex (MTBC), one of the most successful bacterial pathogen groups, remains largely unknown. The study demonstrates that the MTBC comprises two independent clades: one restricted to human M. tuberculosis lineages and another including both animal and human isolates. The authors employed tandem repeat markers and Bayesian statistical analysis of marker variability in infected patients to estimate the MTBC age at approximately 40,000 years.

Abstract

The evolutionary timing and spread of the Mycobacterium tuberculosis complex (MTBC), one of the most successful groups of bacterial pathogens, remains largely unknown. Here, using mycobacterial tandem repeat sequences as genetic markers, we show that the MTBC consists of two independent clades, one composed exclusively of M. tuberculosis lineages from humans and the other composed of both animal and human isolates. The latter also likely derived from a human pathogenic lineage, supporting the hypothesis of an original human host. Using Bayesian statistics and experimental data on the variability of the mycobacterial markers in infected patients, we estimated the age of the MTBC at 40,000 years, coinciding with the expansion of “modern” human populations out of Africa. Furthermore, coalescence analysis revealed a strong and recent demographic expansion in almost all M. tuberculosis lineages, which coincides with the human population explosion over the last two centuries. These findings thus unveil the dynamic dimension of the association between human host and pathogen populations.