Patients with
cystic fibrosis are severely affected by an
infection with Pseudomonas aeruginosa, a microbe known to synthesize
phospholipase C. This study was designed to determine whether that
enzyme would affect the function of
pulmonary surfactant phospholipids. Mucoid and nonmucoid strains of P. aeruginosa, freshly obtained from patients with
cystic fibrosis, were cultured for 12 h on
agar plates. The bacteria were suspended in
saline solution and then pelleted by centrifugation. The supernatant was used to dilute the
surfactant preparation, calf lung
surfactant extract, from 35 to 2 mg/mL.
Surfactant function, before and after incubation, was examined with a capillary surfactometer, an instrument specifically developed for an evaluation of the ability of
surfactant to maintain patency of a narrow glass tube, simulating a terminal conducting airway.
Phospholipid hydrolysis was also evaluated biochemically by determining the total content of
phospholipids in
surfactant before and after incubation. In five experiments, the
lipids were separated with thin-layer chromatography, and the
phosphorus content was determined in the diacylphosphatidylcholine band before and after incubation for 6, 24, and 48 h. Capillary openness and
phospholipid concentration decreased as
enzyme concentration and time of incubation increased (p<0.0001). Linear regression showed a significant correlation between time of capillary openness and
phospholipid concentration (r = 0.957; p<0.0001). Calf lung
surfactant extract hydrolysis was catalyzed by extracts of the bacteria, particularly the nonmucoid, analogous to the catalysis observed with
phospholipase C.
Surfactant hydrolysis catalyzed by
enzymes from P. aeruginosa might severely affect
surfactant function provided
enzyme concentration is high and time of incubation is long.