The virulence in mice of Neisseria meningitidis variants differing in free endotoxin activities and cell envelope properties.

The virulence of two serogroup B meningococcal strains (270E+ and 840E+) having a high endotoxin release during in vitro growth, was compared with the virulence of corresponding variants (270E- and 840E-) liberating less endotoxin. The E-variants were isolated during subcultivations from the E+ strains. 270E+ and 840E+ were both serotype 15:P1.16, while 270E- was serotype 15:P1.2 and 840E- was non-typable. The SDS-PAGE patterns of the E+ and E- variants were also dissimilar. The E+ and E- variants differed in several other properties. Groups of mice were inoculated intravenously (i.v.) or intraperitoneally (i.p.) with E+ and E- meningococci. The endotoxin activities of inoculates and mouse blood were assayed by a Limulus lysate test. The mice received a similar infective dose of E+ and E- variants. A higher level of CFU and endotoxin was found in heart blood of E+ than of E-infected mice during the first hours after infection. Both 30h and 72h after inoculation, E+ variants were significantly more lethal to mice than E- variants (p less than 0.01).