Pseudomonas aeruginosa infection in cystic fibrosis. Bactericidal effect of serum from normal individuals and patients with cystic fibrosis on P. aeruginosa strains from patients with cystic fibrosis or other diseases.

P. aeruginosa strains originating from the respiratory tract of patients with cystic fibrosis (CF) and patients with other diseases (non-CF) were analysed with regard to their sensitivity to the bactericidal activity of human serum. P. aeruginosa strains isolated from CF patients were more sensitive than strains from non-CF patients to the bactericidal activity of normal human serum. The bactericidal activity was heatlabile. As regards the sensitivity to normal human serum, mucoid and non-mucoid variants were not found to differ. Strains originating from chronically infected CF patients with many precipitins against these bacteria did not differ with respect to serum sensitivity from strains originating from intermittently colonized CF patients without P. aeruginosa precipitins. Compared with normal sera, CF sera showed similar or higher bactericidal activity against a panel of P. aeruginosa strains. In this respect, any difference between CF sera with precipitins and CF sera without precipitins against P. aeurginosa was not found. Sera from three CF patients chronically infected with P. aeruginosa, and with many precipitins against these bacteria, showed a selective inability in bactericidal activity against the patients' own P. aeruginosa isolate possibly reflecting the presence of "bactericidal blocking" antibodies.