Effect of surfactant and specific antibody on bacterial proliferation and lung function in experimental pneumococcal pneumonia

Objective: To investigate the effect of surfactant and specific antibody on bacterial proliferation in experimental pneumococcal pneumonia. Methods: Near-term newborn rabbits received a standard dose (10⁷) of type 3 pneumococci via the airways. Control animals were sacrificed 1 minute later. Other animals were ventilated for 5 hours and treated via the tracheal cannula with surfactant (Curosurf 200 mg/kg), a mixture of surfactant and a polyclonal antipneumococcal antibody, the antibody without surfactant, or saline. Results: There was a significant bacterial proliferation in lung tissue in all animals ventilated for 5 hours. Bacterial growth, expressed as log₁₀ colony forming units (CFU) per gram of lung tissue was less prominent in animals treated with a mixture of surfactant and specific antibody than in animals treated with antibody alone (median, 7.51, range, 6.80-7.70 vs. median, 7.92, range, 7.07-8.50; P < 0.05). Dynamic lung-thorax compliance was improved with surfactant or surfactant plus antibody in comparison with saline or antibody alone. Conclusion: The data suggest that the suppressive effect of the antibody on bacterial proliferation becomes evident only when surfactant is administered together with the antibody.