SUMMARY Although Neisseria species other than N gonorrhoeae and N meningitidis normally comprise part of the commensal bacterial flora of the oropharynx, they may occasionally act as opportunistic pathogens. Infections in which these organisms have been implicated include cases of endocarditis, meningitis, septicaemia, otitis, bronchopneumonia and possibly genital tract disease. In this paper, the clinical and pathological features of such infections are described, together with a discusssion of factors that may contribute to their development.In most textbooks of medical microbiology, the genus Neisseria is considered to contain only two pathogenic species, namely, N gonorrhoeae and N meningitidis. The other members of the genus are generally regarded as harmless inhabitants of the oropharynx. There is ample evidence in the literature, however, that these normally non-pathogenic species are capable of producing infection in a variety of anatomical sites including the heart, nervous system, bloodstream, respiratory tract and possibly the genital tract. Although the pathogenesis of gonococcal and meningococcal infections has been investigated extensively and is well documented,' 2 there is little collated information concerning infections produced by other Neisseria spp. This article is an attempt to remedy this deficiency. Classification of the genus NeisseriaAny review of Neisseria infections is complicated by the fact that the classification of the organisms comprising the genus has undergone a number of changes over the years. A detailed discussion of the evolution of the taxonomy of the genus is beyond the scope of this article, but a brief ojitline, which conveys some idea of the degree of change is presented below. In the early part of this century,

Western blot analysis was used to identify antigenic components of Gardnerella vaginalis. Polypeptides bound to nitrocellulose membranes were probed with murine antisera raised to two strains of G. vaginalis, and antibody-antigen complexes were detected with 125I-labelled antimouse immunoglobulin followed by autoradiography. Although there was inter-strain variation in immunogenic polypeptide profiles, all 23 strains of G. vaginalis examined contained a common antigen of molecular mass 41 kDa. This antigen was not found in any of six other bacterial genera.