Neisseria is a genus of Gram (-) bacteria inclued among the proteobacteria, a large group of Gram-negative forms. Neisseria are diplococci that resemble coffee beans when viewed microscopically. 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.