Neisseria /nīser″ē·ə/ [Albert L.S. Neisser, Polish dermatologist, 1855–1916] , a genus of aerobic to facultatively anaerobic bacteria of the family Neisseriaceae. The gram-negative cocci, which appear in pairs with adjacent sides flattened, are among the normal flora of genitourinary and upper respiratory tracts. Pathogenic species include gonococcus and meningococcus forms.
