Pulmonary clearance of Pseudomonas aeruginosa

It has been demonstrated that clearance of 2 strains of Pseudomonas aeruginosa from lungs of normal mice differs from the pattern observed with other gramnegative bacilli. The purpose of this study was to examine the pulmonary clearance of several P. aeruginosa strains and to identify factors responsible for the altered clearance pattern. Mice were nebulized 30 min. via a Henderson aerosol apparatus with 14 P. aeruginosa strains. Three clearance patterns were seen: (1) multiplication of organisms in lungs for one hour after nebulization, followed by progressive clearance; (2) relatively little change in bacterial count of the lungs for 4 hours after nebulization; and (3) progressive clearance. Clearance patterns were not significantly correlated with intraperitoneal LD₅₀, phage, or pyocine type, Hab's "O" serotype, extracellular production of elastase, hemolysin, or protease of the respective pseudomonas strains, or with the histologic picture produced in the lungs. Organisms producing type 1 clearance pattern produced significantly greater amounts of extracellular lecithinase than did other strains. This suggests that alteration of pulmonary surfactant by lecithinase may enable early multiplication of some Pseudomonas strains in lungs, predisposing to pneumonia. Other differences in histologic changes in lungs may be related to yet additional extracellular enzymes of P. aeruginosa.