Pseudomonas-infected cystic fibrosis patient sputum inhibits the bactericidal activity of normal human serum.

Abstract

Sputum samples were obtained from nineteen cystic fibrosis (CF) patients with respiratory tract infections due to Pseudomonas aeruginosa and were examined for the presence of a specific local protective or blocking factor, which might partially explain the inability of CF patients' pulmonary defense mechanisms to clear their lungs of Pseudomonas infection. Using an assay that measures the bactericidal activity of fresh normal human serum (FHS), eighteen of nineteen CF sputa examined were capable of protecting either autologous or heterologous strains of P. aeruginosa from serum bactericidal activity. Most of this protective activity was absorbable at 4 degrees C by Pseudomonas, and could be reduced by dilution in phosphate buffered saline or counteracted by an increase in serum concentration. This protective activity is believed to be due to a Pseudomonas-specific bactericidal blocking antibody. In contrast, only two of 17 non-CF sputa were found to significantly inhibit the bactericidaL activity of FHS for P. aeruginosa. Furthermore, three out of five CF sputa also protected Escherichia coli from the bactericidal activity of FHS. This protective activity was much less than that observed with P. aeruginosa, and was not absorbable at 4 degrees C, suggesting the presence of a second blocking or protective factor in CF sputum. From these observations, we conclude that sputum from CF patients infected with P. aeruginosa contains one or more factors that interfere with the bactericidal activity present in FHS.