Alginate overproduction affects Pseudomonas aeruginosa biofilm structure and function

During the course of chronic cystic fibrosis (CF) infections, Pseudomonas a eruginosa undergoes a conversion to a mucoid phenotype, which is characteri zed by overproduction of the exopolysaccharide alginate. Chronic P. aerugin osa infections involve surface-attached, highly antibiotic-resistant commun ities of microorganisms organized in biofilms. Although biofilm formation a nd the conversion to mucoidy are both important aspects of CF pathogenesis, the relationship between them is at the present unclear. In this study, we report that the overproduction of alginate affects biofilm development on an abiotic surface. Biofilms formed by an alginate-overproducing strain exh ibit a highly structured architecture and are significantly more resistant to the antibiotic tobramycin than a biofilm formed by an isogenic nonmucoid strain. These results suggest that an important consequence of the convers ion to mucoidy is an altered biofilm architecture that shows increasing res istance to antimicrobial treatments.