Desiccation promotes DNA damage and rifampin resistance in Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) is an obligate human pathogen that depends on its ability to spread from host to host to survive as a species. Knowledge of traits supporting transmission is lacking. Here, because desiccation occurs during the generation of Mtb-transmitting aerosol droplets, we exposed Mtb mounted atop a filter platform to varying degrees of humidity to characterize its transcriptomic and metabolomic responses to desiccation and rehydration. Desiccation increased levels of oxidative stress, oxidative damage and double-stranded DNA breaks, activating DNA repair responses required for survival. Expression of the transcription-coupled repair factor, mfd, also increased but this buffered the fitness cost of specific resistance-conferring mutations in rpoB, the target of the frontline drug rifampin. Silencing mfd during aerosolization specifically impaired survival of strains harbouring the most common rifampin resistance allele, S450L. This function is epidemiologically supported by whole-genome sequence analysis of 51,229 clinically circulating strains. These studies suggest that transmission-associated desiccation-induced DNA damage is a potential source of genetic diversification that can potentiate antibiotic resistance.