Neisseria gonorrhoeae and Neisseria meningitidis are pathogenic Neisseria species. N. gonorrhoeae causes the sexually transmitted infection gonorrhea, characterized by urethritis and cervicitis. N. meningitidis most commonly causes meningitis but can also cause septicemia. Both are gram-negative diplococci that can be identified microscopically in clinical samples and cultured on selective media. Treatment involves antibiotics like penicillin, cephalosporins, or tetracyclines.