Ultrastructural studies on the fate of group B meningococci in human peripheral blood leukocytes

Viable, virulent Neisseria meningitidis were rapidly phagocytized by human peripheral blood leukocytes in the presence of 10% autologous blood plasma. Bactericidal activity was detected in the three plasma concentrations tested; however, no loss of viability was observed in 10% plasma during the time required for leukocyte loading. Electron micrographs taken after phagocytosis revealed that most intracellular bacteria were rapidly destroyed; however, some intracellular meningococci remained structurally intact through the 6-h duration of the experiments. Some leukocyte lysis was observed in samples taken 30 min after leukocyte loading. This lysis resulted in the release of apparently intact meningococci, as well as debris from bacteria in various stages of disintegration. Such debris always contained meningococcal ghosts in which the cytoplasmic membrane and outer wall membrane appeared relatively intact. Cells and debris released from lysed leukocytes were enclosed in a membranous sac, presumably the membrane of the phagocytic vacuole.