Pulmonary clearance of gram-negative bacilli

The purpose of this study was to examine the pulmonary clearance of several gram-negative organisms which have been proved clinically important in hospital-aquired pnueumonias and to examine host factors which have been shown to effect the development of gram-negative bacillary pneumonia. Escherichia coli, Proteus mirabilis, Herellea sp., and Flavobacterium sp. were all cleared progressively from the lungs of mice after a 30 minute period of pulmonary deposition by means of an aerosol apparatus. When two separate strains of Pseudomonas were nebulized for 30 minutes, the bacterial count of the lungs was greater 1 hour after nebulization than immediately after the nebulization period; the bacteria were then progressively cleared. This unusual pattern of clearance was not significantly altered by cortisone, tetracycline, starvation, or previous immunization with the challenge strain of pseudomonas. Coinciding with the Pseudomonas clearance, the lung weight increased significantly. Histological studies demonstrated the development and subsequent spontaneous resolution of a mild inflammatory response. When mice were followed for days after a single bacterial nebulization, the lungs were sterile by the ninth day. The differences in pulmonary clearance rates of two strains of the Pseudomonas species from other gram-negative bacilli suggest that a property peculiar to the Pseudomonas cell such as the toxic slime layer may be partially responsible for its propensity to produce noscomial pneumonia.