Neisseria meningitidis

Neisseria meningitidis („meningokok“) z rodu bakterií Neisseria, které patří mezi Gram-negativní koky, je kosmopolitní bakterie, která vyvolává invazivní meningokoková onemocnění (IMO). Přenáší se vzdušnou kapénkovou cestou. Onemocnění začíná většinou náhle v průběhu několika hodin, z plného zdraví vzniká závažný klinický obraz. IMO je i v současné době život ohrožující, úmrtnost se pohybuje kolem 10 %. Nejčastěji bývají postiženy děti mladší pěti let, dospívající a mladí dospělí ve věku 15–25 let.

Morphology and characteristic
Neisseria meningitidis is a Gram-negative diplococcus. They are non-sporulating, mostly encapsulated. They are easily subjected to autolysis, thus losing their characteristic shape and changing their coloring properties. Cultivation-demanding - complex cultivation substrates with protein in native state, CO2, moisture. Cultivation is strictly aerobic. Bacteria produce catalase and oxidase. Acidifie carbohydrates without gas formation. According to their properties, it can be distinguished from other Neisseria. The most important antigen - capsule polysaccharide - protective; can be changed by transformation; during the disease in the blood and cerebrospinal fluid. A total of 13 serogroups are distinguished, with serotypes A, B, C, Y and W135 being the most common worldwide. Cosmopolitan occurrence. Invasive meningococcal disease (IMD) epidemics caused by serogroup A meningococci typically occur in the southern Sahara region. Group B (sporadically) and C (in local epidemics) are more common causes of IMD worldwide, as well as in Europe. IMD cases by groups Y and W135 are growing, especially in countries such as Saudi Arabia, Burkina Faso, some African countries.

Pathogenicity and pathogenesis
It is a natural primary pathogen for humans only. It is transmitted by droplets. Large epidemics are more common in North Africa. In the Czech republick children and adolescents are at highest risk. Virulence factor - serogroup-specific polysaccharide capsule. Except for serogroups A, all other capsular polysaccharides are enriched with sialic acid, which equips bacteria with resistance to alternative pathway of complement activation by reducing the possibility of meningococcal phagocytosis. Antibodies against capsule antigen (as opsonins, in the presence of complement bactericidal).

Etiopathogenesis and symptoms
It is transmitted in air - by droplets. The incubation period is between 1-8 days. N. meningitidis colonizes the nasopharynx and enters the bloodstream (meningococcemia). It manifests as a febrile illness characterized by exhaustion, sever muscle and joint pain, headache, and somnolence (symptoms of intoxication with released endotoxin). Petechiae or suffusions can be present on the skin and they are constantly increasing. A clinical picture of sepsis is formed.

Invasive meningococcal disease may take the form of purulent meningitis, which may be accompanied by vomiting, or impaired consciousness or convulsions. Skin symptoms may not always occur.

Meningococcal sepsis is the most severe form of IMD. Sepsis very soon progresses to septic shock with respiratory and renal failure. Fortunately, this severe sepsis, which almost always ends with death, is rare.

náhled|200px|Nález Gram-negativní Neisseria meningitidis při Gramově barvení likvoru

Laboratory diagnostics
Detection of Neisseria meningitidis is in blood culture or from cerebrospinal fluid (microscopically or by cultivation). Rapid antigen detection is made by bedside cerebrospinal fluid agglutination test. We observe Gram-negative diplococci in a microscopic smear. Other methods include PCR (from blood and cerebrospinal fluid).

Treatments
Intravenously crystalline penicillin, also 3rd generation cephalosporins (cefotaxime, ceftriaxone). Glucocorticoids are used againts endotoxin.

Prevetion
Active immunization by conjugate vaccines (against groups A, C, Y, W) - polysaccharide vaccines for children from two years of age. A vaccine against meningococci type B has been available in the Czech Republic since 4/2014.

Related articles

 * Meningococcal meningitis
 * Invasive meningococcal disease

Reference

 * https://www.vakciny.net/doporucene_ockovani/menab.html
 * Bednář, M., Fraňková, V., Schindler, J., Souček, A., & Vávra, J. (1996b). Lekářská mikrobiologie. Marvil.
 * Bednář, M., Fraňková, V., Schindler, J., Souček, A., & Vávra, J. (1996b). Lekářská mikrobiologie. Marvil.