Gram -ve Cocci

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              Diseases The genus Neisseria contains two important human pathogens: Neisseria meningitidis and Neisseria gonorrhoeae, N meningitidis mainly causes meningitis and meningococcemia.

N gonorrhoeae causes gonorrhea, the second most common notifiable bacterial disease in the United States (Table 16-1).

N meningitidis (meningococcus) has a prominent polysaccharide capsule that enhances virulence by its antiphagocytic action and induces protective antibodies.

N gonorrhoeae (gonococcus) has no polysaccharide capsule but has multiple serotypes based on the antigenicity of its pilus protein.

The endotoxin of N meningitidis is a lipopolysaccharide (LPS) similar to that found in many gram-negative rods, but the endotoxin of N gonorrhoeae is a lipooligosaccharide (LOS).

The growth of both organisms is inhibited by toxic trace metals and fatty acids found in certain culture media, eg, blood agar plates.

A separate genus contains the organism Moraxelta catarrhalis, which is part of the normal throat flora but can cause such respiratory tract infections as sinusitis, otitis media, bronchitis, and pneumonia.

The organisms are transmitted by ajrborne droplets; they colonize the membranes of the nasopharynx and become part of the transient flora of the upper respiratory tract.

The carriage rate is also high in close (family) contacts of patients.

Overall, N meningitidis ranks second to 5 pneumoniae as a cause of meningitis but is the most common cause between the ages of 2 and 18 years.

Resistance to disease correlates with the presence of antibody to the capsular polysaccharide.

Bacteremia can result in the seeding of many organs, especially the meninges.

A presumptive diagnosis of meningococcal meningitis can be made if gram-negative cocci are seen in a smear of spinal fluid.

The differentiation between N meningitidis and N gonorrhoeae is made on the basis of sugar fermentation: meningococci ferment maltose, whereas gonococci do not (both organisms ferment glucose).

Strains resistant to penicillin have rarely emerged, but sulfonamide resistance is common.

Persons with a deficiency of the late-acting complement components (C6-C9) are at risk for disseminated infections, as are women during menses and pregnancy.