Gram-Negative Cocci and Coccobacilli
• Neisseria meningitidis and Neisseria gonorrhoeae are strict human pathogens; other Neisseria species are commonly present on mucosal surfaces.
• Gram-negative, nonmotile, coffee bean–shaped diplococci
• Loosely attached outer membrane that is readily shed, releasing lipooligosaccharide (LOS) into the host
• N. meningitidis enters the respiratory tract, invades mucous membranes, and spreads via the bloodstream.
• Antiphagocytic capsule is important for virulence.
• Released endotoxin induces fever and increases vascular permeability, potentially leading to shock and petechiae (capillary leakage in skin).
• Meningococcal infection is most common in children younger than 5 years of age and in those with deficiency of terminal complement components (C5-C9).
a. Septicemia with or without meningitis
b. Characterized by fever, shock, and generalized hemorrhage ranging from petechiae to purpura
c. Can be rapidly fatal (mortality rate of 25% or higher) if not treated promptly
• Waterhouse-Friderichsen syndrome
a. Complication of meningococcemia
b. Marked by overwhelming disseminated intravascular coagulation and bilateral hemorrhagic adrenal infarctions with septic shock, acute hypotension, tachycardia, and petechiae
• Mild febrile disease with pharyngitis, pneumonia, arthritis, or urethritis
4. Transmission of N. meningitidis
• Person-to-person spread from infected persons
• Inhalation of aerosol droplets (often from asymptomatic posterior nasopharyngeal carriers)
• Breastfeeding infants for the first 6 months of life
• Active immunization of children older than 2 years of age with a polyvalent conjugate, anticapsular vaccine (not effective against serogroup B)
• Postexposure prophylaxis with rifampin, quinolones, or sulfonamides (only if the organism is proved susceptible)
1. Thayer-Martin medium (selective chocolate agar)
• Used for isolating N. gonorrhoeae in specimens from nonsterile areas, such as the cervix and urethra
• Contains vancomycin (kills gram-positive bacteria), colistin (kills gram-negative bacteria except Neisseria species), and nystatin (kills fungi)
• Pili (fimbriae) and outer membrane protein II (OMPII) promote adherence to and invasion of mucosal cells.
• IgA protease cleaves secretory IgA, reducing host defense to gonococcal infection.
