Electron microscopical study of Neisseria meningitidis releasing various amounts of free endotoxin

A study has been made of the ultrastructure of four strains of Neisseria meningitidis which liberate varying amounts of free endotoxin in a chemically-defined, protein-free medium. The two strains which did not release detectable or only sparse amounts of free, filtrable endotoxin were rather uniform in cell size. Their cells appeared to be intact and showed a low tendency to aggregate, In addition cells of these strains showed only sporadic loose, trilaminar membranes and blebs, and free membranous structures were sparse in the medium. The endotoxin releasing strains liberated a high yield of free structures from the outer cell wall into the medium. These structures may represent the lipopolysaccharide (LPS).