Despite Antagonism , Enhances Colonization in a Murine Lung Infection Model.

and are prevalent lung pathogens in cystic fibrosis (CF). Whereas co-infection worsens the clinical outcome, prototypical strains are usually antagonistic . We sought to resolve the discrepancy between these and observations. , growth kinetics for co-cultures of co-isolates from CF patients showed that not all strains affected viability. On solid media, slow-growing colonies were visualized around some strains whether or not viability was reduced in liquid co-cultures. The interactions were then characterized in a mouse lung infection model. Lung homogenates were plated on selective media allowing colony counts of either bacterium. Overall, 35 and 10 strains (clinical, reference, and mutant strains), for a total of 200 co-infections, were evaluated. We observed that colonization of lung tissues was promoted by and even by strains showing antagonism . Promotion was proportional to the extent of colonization, but no correlation was found with the degree of myeloperoxidase quantification (as marker of inflammation) or with specific virulence-associated factors using known mutant strains of and . On the other hand, significantly increased the expression of two possible cell receptors for , ., ICAM-1 and ITGA-5 (marker for integrin αβ) in lung tissue, while mono-infections by did not. This study provides insights on polymicrobial interactions that may influence the progression of CF-associated pulmonary infections.