ABSTRACT
N. meningitidis (Nm) is a capnophilic, gram-negative coffee-bean shaped diplococcus that is oxidase-positive, catalase-positive, and produces acid from glucose and maltose by oxidation. The bacterium is an obligate human pathogen carried episodically in the nasopharynx and mostly exists in a commensal relationship with the host. Carriage is most frequent in adolescents and young adults and horizontal transmission, effected by respiratory droplets, is facilitated by close (kissing) contact. Nm has a typical gram-negative envelope, but the outer leaflet of the outer membrane (OM) contains lipooligosaccharide (LOS) instead of lipopolysaccharide (LPS). The core polysaccharide of LOS undergoes antigenic variation exposing a variety of epitopes on the cell surface. Also, the cell surface is decorated with pili which enable initial adhesion to mucosa, and which undergo antigenic and phase variation. Opacity-associated proteins (Opa) are important in the ability of the organism to adhere tightly to epithelia and factor H-binding protein to down-regulate the alternative pathway of the complement cascade. The most important virulence determinant of Nm is the production of a capsule. An effective adaptive host immune response depends on an intact complement system, bactericidal antibodies and the spleen. The onset of meningococcemia may be insidious and can result in several outcomes ranging from a short episode of febrile, flu-like symptoms to septicemia and meningitis. A hemorrhagic rash develops in about 80% of bacteremic patients, which begins as petechiae that occur initially on the extremities and trunk but may progress to involve any part of the body. As meningococcemia proceeds, pustules, bullae, and hemorrhagic lesions with central necrosis may develop. Fulminant meningococcal sepsis (FMS), comprising shock and disseminated intravascular coagulation (DIC), occurs within a matter of hours, which may or may not be accompanied by meningitis. Empiric antimicrobial therapy should begin urgently. The antibiotic of choice is IV ceftriaxone or cefotaxime for five to seven days. Chloramphenicol is an alternative patients with hypersensitivity to β-lactam antibiotics. The duration of antibiotic therapy is usually for five to seven days but can extend to 21 days.
