Influence of mucoid coating on clearance of Pseudomonas aeruginosa from lungs

Pulmonary infection with mucoid strains of Pseudomonas aeruginosa in present in the majority of cystic fibrosis patients with chronic lung disease. It has been postulated that this mucoid coating may act to decrease lung clearance of Pseudomonas by limiting access of phagocytes, antibodies, and antibiotics to the bacteria. To determine whether mucoid coating of Pseudomonas might decrease intrapulmonary killing, groups of guinea pigs were infected with intrabronchial instillations of equivalent numbers of mucoid and nonmucoid Pseudomonas. For this study, mucoid strains of Pseudomonas were obtained from cystic fibrosis sputa and passaged on blood agar plates to obtain their nonmucoid revertants. Animals were then sacrificed at timed intervals after infection, and quantitative cultures were performed on lung homogenates. In all cases, mucoid challenge strains retained their mucoid morphology after passage in guinea pig lungs. No difference in killing of mucoid and nonmucoid Pseudomonas could be detected at 6, 24, or 48 h after lung infection. Further challenge studies used guinea pigs that were either prevaccinated with lipopolysaccharide P. aeruginosa vaccine or else treated with tobramycin sulfate after infection. Nonvaccinated or untreated controls had reduced intrapulmonary killing of Pseudomonas compared with vaccinees or treated groups (P < 0.02 and P < 0.01, respectively). However, there were no differences in pulmonary killing of mucoid and nonmucoid Pseudomonas in the presence of either specific antibodies or antibiotic. We conclude from these studies that mucoid coating of Pseudomonas does not selectively impede mechanisms of intrapulmonary killing in guinea pig lungs.