GROUP-B STREPTOCOCCAL BETA-HEMOLYSIN EXPRESSION IS ASSOCIATED WITH INJURY OF LUNG EPITHELIAL-CELLS

Group B streptococci (GBS) are the leading cause of serious bacterial infection in newborns. Early onset disease is heralded by pneumonia an d lung injury, and the lung may serve as a portal of entry for GBS int o the bloodstream. To examine a potential role for GBS beta-hemolysin in lung epithelial injury, five wild-type strains varying in beta-hemo lysin expression were chosen, along with five nonhemolytic (NH) and fi ve hyperhemolytic (HH) variants of these strains derived by chemical o r transposon mutagenesis. Monolayers of A549 alveolar epithelial cells were exposed to log-phase GBS or stabilized hemolysin extracts of GIB S cultures, and cellular injury was assessed by lactate dehydrogenase (LDH) release and trypan blue nuclear staining. Whereas NH strains pro duced no detectable injury beyond baseline (medium alone), hemolysin-p roducing strains induced LDH release from A549 cells in direct correla tion to their ability to lyse sheep erythrocytes. HH strains were also associated with marked increases in trypan blue nuclear staining of A 549 monolayers. The extent of LDH release produced by HH strains was s ignificantly reduced in the presence of dipalmitoyl phosphatidylcholin e, a known inhibitor of hemolysin and the major phospholipid component of human surfactant. Electron microscopic studies of A549 cell monola yers exposed to HH GBS mutants revealed global loss of microvillus arc hitecture, disruption of cytoplasmic and nuclear membranes, and marked swelling of the cytoplasm and organelles. We conclude that GBS hemoly sin expression correlates with lung epithelial cell injury and may be important in the initial pathogenesis of early-onset disease, particul arly when pulmonary surfactant is deficient.