Chronic Coinfection with Pseudomonas aeruginosa and Normal Colony Staphylococcus aureus Causes Lung Structural Damage in the Cystic Fibrosis Rat.

Cystic fibrosis (CF) respiratory outcomes are heavily influenced by complications of infection. Pseudomonas aeruginosa and Staphylococcus aureus are the most common colonizers of the cystic fibrosis lung, and frequently overlap to cause chronic and persistent coinfections associated with severe disease. However, the dynamics of P. aeruginosa and S. aureus coinfection and its impacts on the development of CF lung structural damage are poorly understood. Additionally, small colony variants (SCVs) of S. aureus have been associated with P. aeruginosa infections in people with CF, but their role in disease progression is largely unknown. In this work, the CF rat was used to model chronic lung coinfection with P. aeruginosa and S. aureus, using clinically and laboratory-derived normal colony and SCV strains of S. aureus to evaluate the impact of phenotype on clinical outcomes. Rats coinfected with clinically derived S. aureus of both phenotypes experienced increased inflammation in the lung. However, only the combination of P. aeruginosa and clinically normal colony S. aureus led to lung structural decline, including mucus obstruction and bronchiectasis. Regression analyses showed that the damage was associated with a higher burden of P. aeruginosa. These data indicate that chronic coinfection with normal colony S. aureus and P. aeruginosa may support the progression CF lung decline driven by P. aeruginosa, which might be avoided when coinfecting S. aureus exhibits the SCV phenotype.