ABSTRACT
A rabbit model of bacterial pneumonia induced by intratracheal administration of 1 x 108 cfu P. aeruginosa was developed. Several parameters including bacterial numbers in the lungs, blood and spleen tissues, histopathology, levels of selected cytokines in bronchoalveolar lavage fluids [BALF] and arterial blood gas analyses to compare the severity of pneumonias caused by the wild type P. aeruginosa were measured over 4 h to that of its isogenic OprF mutant. The rabbits were able to clear most of the bacteria from the airways, but both strains were able to disseminate to distant organs as confirmed by the detection of bacteria in peripheral blood samples and splenic tissue. The lungs were free from alveolar edema as judged by the histologic assessment. However, arterial blood gas analyses showed a significant change in O2 saturation and gas exchange, indicating a lower level of lung injury in animals treated with the mutant strain. Likewise, BALF from animals challenged with mutant strains demonstrated lower numbers of white blood cells than the wild type group. While, the histologic appearance of pneumonia induced by the OprF-deficient and the wild type P. aeruginosa was comparable in this model, the observed differences in alveolar gas exchange and inflammatory cell traffic may derive from the presence or absence of OprF at the bacterial surface