Neisseria – two members of this genus are of medical importance.

• Characteristics: gram-negative diplococci; pathogenic strains are usually encapsulated and are very fastidious, requiring enriched media and growth in an atmosphere rich in CO2.

• Virulence factors:

  • Fimbriae and capsules – aid in attachment to mucous membranes and resistance to phagocytosis.

  • LPS (endotoxin) – released from cell envelopes following cell lysis; causes fever, hemorrhage, inflammation, abortion, and toxic shock.

  • Protease – destroys secretory antibody (Ig A) on the surface of mucous membrane.

  • Penicillinase – destroys penicillin.

• N. gonorrhoeae – almost always an STD (sexually transmitted disease) except for neonatal cases where the newborn infant is infected as it passes through the birth canal. Organisms attach to mucous membranes of the urethra, vagina, eyes, throat, etc. and then invade the underlaying connective tissue. In some cases, the organisms may enter the blood and be spread to the joints (leading to a form of arthritis) or to the endocardium or meninges. Gonococcal infections of the eyes can lead to blindness. All newborn infants are given eyedrops containing silver nitrate or antibiotics as a preventative measure to prevent opthalmia neonatorum.

  • Immunization – none available at present and infections does not produce lasting immunity, leading to recurrent infections.

  • Chemotherapy – penicillin has been the drug of choice but penicillinase-producing strains have become more prevalent. Chance of multiple STDs (especially syphilis and chlamydiosis) in addition to the gonorrhea may require a combination of antibiotics.

• N. meningitidis – cause epidemic meningococcal meningitis. Carriers harbor the organism in their nasopharynx and pass it to others by droplets. After an initial bout of pharyngitis, the organism in some cases will enter blood and migrate to the meninges causing a potentially lethal condition.

  • Immunization – most people are naturally immune, probably due to exposure when young. A vaccine made from capsular polysaccharides is available that is effective against most strains. It is probably used during epidemics on individuals who may have been exposed to the disease.

  • Chemotherapy – penicillin or, for those allergic to penicillin, chloramphenicol. Rifampin or tetracycline are used prophylactically for those who have come in close contact with someone with the disease.