Role of alginate O acetylation in resistance of mucoid Pseudomonas aeruginosa to opsonic phagocytosis

Establishment and maintenance of chronic lung infections with mucoid Pseudo monas aeruginosa in patients with cystic fibrosis (CF) require that the bac teria avoid host defenses. Elaboration of the extracellular, O-acetylated m ucoid exopolysaccharide, or alginate, is a major microbial factor in resist ance to immune effecters. Here we show that O acetylation of alginate maxim izes the resistance of mucoid P. aeruginosa to antibody-independent opsonic killing and is the molecular basis for the resistance of mucoid P. aerugin osa to normally nonopsonic but alginate-specific antibodies found in normal human sera and sera of infected CF patients. O acetylation of alginate app ears to be critical for P. aeruginosa resistance to host immune effecters i n CF patients.