Neisseria spp. Overview and Key Characteristics

Neisseria spp. (Gram-negative cocci)

• Neisseria contains two important human pathogens: N. meningitidis and N. gonorrhoeae.
• N. meningitidis causes meningitis and meningococcemia, characterized by purpuric lesions (Figure 1).
• N. gonorrhoeae causes gonorrhea, neonatal conjunctivitis (ophthalmia neonatorum) (Figure 2), and pelvic inflammatory disease (PID).
• N. meningitidis is also known as the meningococcus.
• N. gonorrhoeae is also known as the gonococcus.

Important Properties of Neisseria

• Gram-negative cocci, resembling paired kidney beans.
• Growth inhibited by certain trace metals and fatty acids in culture media.
• Cultured on chocolate agar (blood agar heated to 80°C).
• Oxidase-positive (possessing cytochrome c enzyme). Colonies exposed to phenylenediamine turn purple or black.

N. meningitidis

• Has a polysaccharide capsule (Table 3).
• Divided into serogroups (at least 13) based on capsular polysaccharide antigenicity.
• Five serotypes (A, B, C, Y, and W-135) cause most cases of meningitis and meningococcemia.
• Serotype A is the leading cause of epidemic meningitis.

N. gonorrhoeae

• Lacks a polysaccharide capsule.
• Multiple serotypes based on pilus protein antigenicity (over 100 known).
• Has three outer membrane proteins (I, II, and III) that play a role in cell attachment.
• Protein II displays antigenic variation.

Neisseria Endotoxin

• Neisseria contain endotoxin (lipooligosaccharide, LOS) in their outer membrane.

Pathogenesis and Epidemiology (N. meningitidis)

• Humans are the only natural hosts for N. meningitidis.
• Transmitted via airborne droplets.
• Colonizes the nasopharynx.
• Carriers can be asymptomatic.
• Can disseminate into the bloodstream, meninges, joints, etc.
• Carriage rate can be high in close quarters (up to 35%).

N. meningitidis Virulence Factors

• Polysaccharide capsule (resists phagocytosis by PMNs).
• Endotoxin (causes fever, shock).
• Immunoglobulin A (IgA) protease (affects bacterial attachment).

Laboratory Diagnosis

• Smear and culture of blood and spinal fluid samples.
• Immunofluorescence can be helpful.
• Nucleic acid amplification tests are used for screening.

Treatment

• Penicillin G is the treatment of choice for meningococcal infections.
• Ceftriaxone can be used as an alternative, especially if allergies to penicillin exist.

Prevention

• Chemoprophylaxis (rifampin, ciprofloxacin).
• Immunization (capsular polysaccharide of groups A, C, Y, and W-135).

Pathogenesis and Epidemiology (N. gonorrhoeae)

• Primarily a sexually transmitted infection.
• Colonizes mucous membranes (genital, anal, pharyngeal).
• Pili (important virulence factors): mediate attachment to host cells.
• Lipooligosaccharide (LOS) and outer membrane proteins also contribute to virulence.
• IgA protease: degrades IgA, hindering immune response.

Laboratory Diagnosis (N. gonorrhoeae)

• Gram staining and culture of discharge.
• Nucleic acid amplification tests, are increasingly utilized for screening.

Treatment (N. gonorrhoeae)

• Ceftriaxone is the treatment of choice.
• Alternatives (azithromycin, ciprofloxacin) are available for penicillin or cephalosporin allergies.

Prevention (N. gonorrhoeae)

• Treatment of symptomatic patients.
• Detection of asymptomatic carriers (a major problem).
• Use of erythromycin ointment for prevention of gonococcal conjunctivitis in newborns.