Immunological and epidemiological evidence suggests that the development of natural immunity to meningococcal disease results from colonization of the nasopharynx by commensal Neisseria spp., particularly with N. lactamica. We report here that immunization with N. lactamica killed whole cells, outer membrane vesicles, or outer membrane protein (OMP) pools and protected mice against lethal challenge by a number of diverse serogroup B and C meningococcal isolates in a model of bacteremic infection. Sera raised to N. lactamica killed whole cells, OMPs, or protein pools were found to cross-react with meningococcal isolates of a diverse range of genotypes and phenotypes. The results confirm the potential of N. lactamica to form the basis of a vaccine against meningococcal disease.

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SUMMARYAerosol infection (Al) of Porton outbred mice with Listeria species, exhibiting varying degrees of virulence, was compared with gastric intubation (GI) on the basis of numbers of deaths, 50% lethal dose (LD50) and pattern of listerial infection. The Al route appeared to be more sensitive, efficient and consistent than GI in that it required 105 fewer micro-organisms to obtain infection and death then ensued within 4 days, with GI deaths usually occurring on day 7. All the virulent strains tested caused 100 % mortality by AI, while virulent and avirulent strains were indistinguishable by GI. Bacterial counts in the livers and spleens of infected mice were consistent with the relative virulence of the infectious agent using AI but not in GI mice. There were higher numbers of micro-organisms and more widespread lesions in the organs of AI mice than in GI. Results indicate that Al is an accurate in vivo indicator of virulence in listeria and using Al, bacterial counts in the liver and spleen could replace LD50 tests, thereby reducing the number of animals required for in vivo virulence testing.