Experimental system enables studies of Mycobacterium tuberculosis during aerogenic transmission.

Tuberculosis, a persistent public health challenge worldwide, is transmitted when exhaled Mycobacterium tuberculosis (Mtb) particles expelled from an infected individual are inhaled by a susceptible person. To study the adaptation of Mtb during transition between hosts, we developed a transmission simulation system (TSS) that combines controlled pathogen aerosolization and measurement of bioaerosol particle characteristics with in-flight sampling of Mtb and infection of mice by nose-only exposure. Using scattered-light spectrometry, we demonstrated that Mtb aerosol concentrations generated by the TSS better represented human cough than the aerosol concentrations produced by a full-body inhalation exposure system commonly used for Mtb infection of mice. Additionally, the TSS deposited clinically relevant low doses of Mtb into murine lungs with greater precision than the full-body inhalation exposure systems. The TSS revealed a linear correlation between Mtb inoculum concentration and pathogen deposition in murine lungs up to 200 colony-forming units. Higher inoculum concentrations led to a reduction in total particle number, which resulted in disproportionately lower pulmonary infection doses. Importantly, the particle size distributions of Mtb-laden aerosols produced by the TSS mirrored those of tuberculosis patient coughs, with 90% of culturable Mtb found in particles with aerodynamic diameters below 3.3 µm. In conclusion, the TSS represents a novel effective and precise translational platform enabling detailed biophysical and molecular studies of Mtb transmission.

Importance: Tuberculosis is transmitted when exhaled Mycobacterium tuberculosis (Mtb)-laden microdroplets of an infected individual are inhaled by a susceptible person. Historically, studies on Mtb transmission have focused mainly on epidemiology due to the technical challenges in replicating the transmission process effectively in a laboratory setting. In this study, we introduce a transmission simulation system (TSS) that integrates controlled Mtb aerosolization, biophysical aerosol particle measurements, in-flight Mtb sampling, and aerosol infection of mice. The TSS generated Mtb bioaerosol concentrations comparable to those produced by human coughs. These pathogen droplets were accurately deposited in mouse lungs at low Mtb doses relevant to human transmission. Notably, the distribution of Mtb among aerosol particles of various sizes closely mirrored that found in the coughs of tuberculosis patients. In summary, the TSS represents a novel tool for conducting molecular studies of Mtb transmission through the air.