Role of Pseudomonas aeruginosa pili in acute pulmonary infection.

The role of piliation in the development and course of acute pulmonary infection was examined using infant BALB/cByJ mice inoculated by intranasal instillation of isogenic Pil+ and Pil- mutants of Pseudomonas aeruginosa PA1244, PAK, and PAO1. The piliated strains caused more cases of pneumonia, bacteremia, and mortality than the nonpiliated strains (chi-square analysis, alpha = 0.001). The piliated strains were more often associated with severe diffuse pneumonias, while the nonpiliated organisms resulted in less severe, focal pneumonias, although these differences did not achieve statistical significance. Purified pilin protein used to inoculate the mice resulted in local inflammatory changes. The nonpiliated strain PA1244-NP was as virulent as the piliated strain PAO1, suggesting that expression of other virulence factors are also important in the development of acute pneumonia. This infant mouse model of pulmonary infection appears to be a useful system for the analysis of P. aeruginosa virulence factors involved in the pathogenesis of pneumonia.