The genus Neisseria contains a number of species which are normal flora and pathogens of humans and animals. Of these species, the species of human origin, and particularly the pathogenic species, N. gonorrhoeae and N. meningitidis, have been studied extensively in an effort to control the infections they cause. Gonorrhea, caused by N. gonorrhoeae, is one of the most frequently reported infectious diseases in the United States and worldwide. Of the Neisseria and related species, only N. gonorrhoeae is considered always to be pathogenic i.e., cause disease. N. gonorrhoeae is not considered to be normal flora under any circumstances.
Meningococcus; Neisseria meningitidis