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. 