Mycobacteria develop biofilms on airway epithelial cells and promote mucosal barrier disruption

Tuberculosis displays several features commonly linked to biofilm-associated infections, including recurrence of infection and resistance to antibiotic treatment. The respiratory epithelium represents the first line of defense against pathogens such as Mycobacterium tuberculosis (Mtb). Here, we use an air-liquid interface model of human primary bronchial epithelial cells (PBEC) to explore the capability of four species of mycobacteria (Mtb, M. bovis (BCG), M. avium, and M. smegmatis) to form biofilms on airway epithelial cells. Mtb, BCG, and M. smegmatis consistently formed biofilms with extracellular matrixes on PBEC cultures. Biofilms varied in biomass, matrix polysaccharide content, and bacterial metabolic activity between species. Exposure of PBEC to mycobacteria caused the disruption of the epithelial barrier and was accompanied by mostly apical non-apoptotic cell death. Structural analysis revealed pore-like structures in 7-day biofilms. Taken together, mycobacteria can form biofilms on human airway epithelial cells, and long-term infection negatively affects barrier function and promotes cell death.