The pulmonary clearance of smooth and rough strains of Pseudomonas aeruginosa

Upper airway colonization with rough strains of Pseudomonas is associated with clinical deterioration in patients with cystic fibrosis. These rough strains are less toxic than smooth strains in the burned mouse model and in vitro assays. We measured the 4-h pulmonary clearance of 10⁴ and 10⁶ rough and smooth Pseudomonas after intrabronchial inoculation. After 10⁴ Pseudomonas, rough strains were cleared more efficiently than smooth strains (89 ± 13% versus 140 ± 19% of the original inoculum, respectively, p < 0.05). This was associated with more total bronchoalveolar lavage PMNs after inoculation with rough as compared with smooth Pseudomonas (1.60 ± 0.38 x 10⁵ versus 0.55 ± 0.09 x 10⁵, respectively, p < 0.05). After inoculation with 10⁶ Pseudomonas, rough were cleared less efficiently than smooth Pseudomonas (380 ± 45% versus 134 ± 12% of the original inoculum, respectively, p < 0.05). There was no difference in the BAL PMNs of the animals inoculated with either bacterial strain at this inoculum (8.1 ± 0.6 x 10⁵ and 9.4 ± 1.0 x 10⁵ for the rough and smooth Pseudomonas, respectively). When PMN differences were abolished in C5-deficient mice, 10⁴ rough were cleared less efficiently than smooth Pseudomonas. The relatively poor clearance of rough Pseudomonas could not be explained by in vitro differences in PMN killing of BAL toxicity or by intrinsic growth rates.