Lipid peroxidation of lung surfactant by bacteria

The epithelium of the lung is lined with extracellular pulmonary surfactant. This is the surface that invading bacteria first come into contact with when they enter the alveoli. As bacteria become established and interact with this layer, various characteristics of surfactant may become altered. We studied free radical production by three bacterial species, group B streptococci, Escherichia coli, and Pseudomonas aeruginosa, as well as the effect of two concentrations of lung surfactant (Curosurf at 0.04 and 0.4 mg/ml) on this production estimated by the nitro blue tetrazolium reduction test. We also measured the lipid peroxidation of surfactant at various incubation times (0-20 h), using a LPO-586 test kit. In addition, the effect of vitamin E as an antioxidant in a concentration of 0.5 M was determined by the lipid peroxidation test. We found that the nitro blue tetrazolium reduction by the three bacterial species and lipid peroxidation of lung surfactant increased with time. Vitamin E reduced the lipid peroxidation of this surfactant. By measuring bacterial growth at various incubation times we showed that lung surfactant was bactericidal to group B streptococcal and E. coli strains and that P. aeruginosa strains were resistant to surfactant. We conclude that bacteria, probably by their production of reactive oxygen species, cause lipid peroxidation of lung surfactant.