Neisseria is a genus of bacteria, included among the proteobacteria, a large group of Gram-negative forms. Neisseria are diplococci which resemble coffee beans when viewed microscopicaly. The genus includes the species N. gonorrhoeae (also called the gonococcus), which causes gonorrhoea, and N. meningitidis (also called the meningococcus), one of the most common causes of bacterial meningitis, and the causative agent of meningococcal septicaemia.