The effect of alginate on the invasion of cystic fibrosis respiratory epithelial cells by clinical isolates of pseudomonas aeruginosa

Chronic infection in the cystic fibrosis (CF) lung is characterized by Pseu domonas aeruginosa strains that overproduce the mucoid exopolysaccharide, a lginate. Previous experiments have shown that long-term survival of P. aeru ginosa in the CF lung may be facilitated by increased adherence and decreas ed invasion of respiratory epithelial cells. Therefore, mucoid and nonmucoi d clinical isolates of P. aeruginosa were assayed for their ability to asso ciate with and invade the CF respiratory epithelial cell line, CF/T43 Assoc iation assays and gentamicin exclusion assays demonstrated that mucoid P. a eruginosa associates with and invades CF/T43 cell monolayers significantly less than nonmucoid P. aeruginosa strains (P =.004,.02). Fluorescence micro scopy invasion assays confirmed these results. The differences in associati on and invasion by the P. aeruginosa strains were not due to differences in lipopolysaccharide phenotype or cytotoxicity for CF/T43 respiratory epithe lial cells. Exogenous bacterial alginate had no effect on the invasion of C F respiratory epithelia by a nonmucoid strain. Invasion assays with the wil d-type P. aeruginosa strain PAO1 end isogenic algU end mucA mutant strains failed to show differences in invasion (P = .25). We conclude that (i) muco id P. aeruginosa isolates associate with and invade CF/T43 respiratory epit helial cells with less efficiency than nonmucoid P, aeruginosa, (ii) these differences are not due to variations in lipopolysaccharide phenotype betwe en strains, (iii) neither exogenous nor endogenous alginate affects the abi lity of P, aeruginosa to invade CF/T43 respiratory epithelial cells, and (i v) invasion of CF/T43 respiratory epithelial cells by a laboratory referenc e strain of P. aeruginosa does not appear to be regulated by AlgU.