No abstract

Recent evidence suggests that colonization of the upper respiratory tract by gram-negative bacilli is mediated by adherence to regional epithelial cells. Buccal epithelial cells were obtained for study from 12 seriously ill patients, all of whom were colonized with Pseudomonas aeruginosa. In comparison to cells from uncolonized controls, cells obtained from these patients attached significantly more P. aeruginosa organisms during incubation in vitro. Although the sialic acid content of colonized patients' cells was less than that of controls' cells, removal of sialic acid from normal cells with neuraminidase did not increase bacillary adherence. Trypsinization of normal cells increased bacillary adherence and significantly reduced the amount of fibronectin on the cell surface. Both trypsinized normal cells and cells recovered from seriously ill colonized patients attached large numbers of P. aeruginosa organisms in vitro and demonstrated decreased fibronectin on the cell surface by immunofluorescent staining. These findings suggest that the host alteration associated with increased susceptibility to adherence by P. aeruginosa is the loss of fibronectin from the cell surface.

Sera from 33 patients with cystic fibrosis and two pediatric patients being treated for chronic pulmonary infections not related to cystic fibrosis and six sera or serum pools from uninfected individuals were tested with a microtiter radioimmunoassay for reactivity against exotoxin A and two proteases from Pseudomonas aeruginosa. Exotoxin A was purified from a low-protease strain of P. aeruginosa and shown to have adenosine diphosphate-ribose transferase activity and mouse lethality. Proteases were purified from an isolate of P. aeruginosa from a patient with cystic fibrosis and had proteolytic activity against elastin and collagen in an assay employing dimethylated protein substrates. The antibody responses of the patients detected using 125I-labeled antibody to human immunoglobulin were correlated with clinical evaluations expressed as a composite score based on pulmonary findings, case histories, growth and nutrition, and chest X rays. Values in the radioimmunoassay for patients' sera were compared with those of a control serum pool and expressed as the ratio of counts per minute (cpm) in patient serum to the cpm in the control pool. Inverse correlations were found between these ratios for each of the pseudomonas exoproducts and clinical scores; highest ratios occurred in patients showing the lowest clinical scores. These results confirm that proteases and exotoxin A of P. aeruginosa are produced in cystic fibrosis pulmonary infections due to P. aeruginosa and suggest that they may serve as significant virulence factors in these chronic infectious states.