Mycobacterium abscessus biofilms have viscoelastic properties which may contribute to their recalcitrance in chronic pulmonary infections

Mycobacterium abscessus is emerging as a cause of recalcitrant chronic pulmonary infections, particularly in people with cystic fibrosis (CF). Biofilm formation has been implicated in the pathology of this organism, however the role of biofilm formation in infection is unclear. Two colony-variants of M. abscessus are routinely isolated from CF samples, smooth (Ma(Sm)) and rough (Ma(Rg)). These two variants display distinct colony morphologies due to the presence (Ma(Sm)) or absence (Ma(Rg)) of cell wall glycopeptidolipids (GPLs). We hypothesized that Ma(Sm) and Ma(Rg) variant biofilms might have different mechanical properties. To test this hypothesis, we performed uniaxial mechanical indentation, and shear rheometry on Ma(Sm) and Ma(Rg) colony-biofilms. We identified that Ma(Rg) biofilms were significantly stiffer than Ma(Sm) under a normal force, while Ma(Sm) biofilms were more pliant compared to Ma(Rg), under both normal and shear forces. Furthermore, using theoretical indices of mucociliary and cough clearance, we identified that M. abscessus biofilms may be more resistant to mechanical forms of clearance from the lung, compared to another common pulmonary pathogen, Pseudomonas aeruginosa. Thus, the mechanical properties of M. abscessus biofilms may contribute to the persistent nature of pulmonary infections caused by this organism.