Transmissible Mycobacterium tuberculosis Strains Share Genetic Markers and Immune Phenotypes

Abstract

RATIONALE: Successful transmission of tuberculosis depends on the interplay of human behavior, host immune responses and Mycobacterium tuberculosis virulence factors. Previous studies have focused on identifying host risk factors associated with increased transmission, while the contribution of specific genetic variations in mycobacterial strains themselves are still unknown. OBJECTIVES: To identify mycobacterial genetic markers associated with increased transmissibility, and examine whether these markers lead to altered in vitro immune responses. METHODS: Using a comprehensive (n = 10,389) tuberculosis registry and strain collection in the Netherlands, we identified a set of 100 M. tuberculosis strains either least or most likely to be transmitted after controlling for host factors. We subjected these strains to whole genome sequencing and evolutionary convergence analysis. We repeated this analysis in an independent validation cohort. A subset of the original strains was used to perform functional immunological experiments to measure in vitro cytokine production and neutrophil responses to strains with or without the identified mutations associated to increased transmissibility. MEASUREMENTS AND MAIN RESULTS: We identified the loci espE, PE-PGRS56, Rv0197, Rv2813-2814c and Rv2815-2816c as targets of convergent evolution among transmissible strains. We validated four of these regions in an independent set of strains, and demonstrated that mutations in these targets affected in vitro monocyte and T-cell cytokine production, neutrophil reactive oxygen species release and apoptosis. CONCLUSIONS: This study identifies genetic markers in convergent evolution of M. tuberculosis towards enhanced transmissibility in vivo that are associated with altered immune responses in vitro.