Neisseria meningitidis
Capsule is a virulence factor, due to its antiphagocytic properties.
Serogroup B strains are a predominant cause of meningococcal disease. The serogroup B capsular polysaccharide is a
homopolymer of alpha-2,8 polyneuraminic acid and is poorly immunogenic (other capsular polysaccharides are immunogenic in
humans).  Serogroup B capsular polysaccharide is also chemically and immunologically identical to capsular polysaccharide in
Escherichia coli K-1 and surface polysaccharide of Moraxella nonliquefaciens strains.

N. gonorrhoeae and N. meningitidis pilli are antigenically and structurally similar.  Pili also mediate the attachment of N. meningitidis
to nasopharyngeal cells.

N. gonorrhoeae and N. meningitidis possess several outer membrane proteins that have been studied at the molecular level and
found to be analogous to one another.

Produce IgA1-protease, which degrades and inactivates immunoglobulin of the IgA1 subtype found in mucosal secretions and serum.
Colonies of are larger than those of gonococci (1.0 mm in diameter) and are smooth
and moist with a glistening surface and entire edge. The capsule is responsible of
mucoid colonies.  Due to autolysis with age, colonies become more butyrous and
Primary isolation is made on blood agar, chocolate agar, or Mueller-Hinton agar. A 3-
10% CO
2 atmosphere and high relative humidity enhances growth. Optimal growth
temperatures is 36-37 ºC. Non-hemolytic. A selective medium such as modified
Thayer-Martin medium may be used for isolation too. Does not resist in old cultures
(autolysis) or to prolonged passages. Dies quickly when storaged at 4 ºC.
Fastidious. Requires mineral salts, lactate, a few amino acids, and glutamic acid as
a carbon source. Cystine is required by approximately 10% of the strains, and some
strains can be adapted to grow with ammonium salts as the sole nitrogen source.
Sugars fermentation should be tested in cysteine trypticase agar containing sugars
(glucose, maltose, sucrose etc.) at a final concentration of 1-2%.
Cultural characteristics
Biochemical characters
Phylum Proteobacteria, Class Betaproteobacteria, Order Neisseriales, Family Neisseriaceae, Genus Neisseria, Neisseria meningitidis
(Albrecht and Ghon 1901) Murray 1929. Common name: "meningococcus".

Old synonyms:
Diplokokkus intracellularis meningitidis Weichselbaum 1887, Neisseria weichselbaumii Trevisan 1889, Micrococcus
(Jaeger) Migula 1900, Micrococcus meningitidis cerebrospinalis Albrecht and Ghon 1901, Micrococcus meningitidis
Albrecht and Ghon 1903.

Serogrouping of is based on antigenic differences in capsular polysaccharides, and presently recognized serogroups include A, B, C, H,
I, K, L, X, Y, Z, W135, and 29E.
Gram-negative cocci, grouped in pairs. Non-motile. Flagella are absent. Capsule is produced. Fimbriae (pilli) are present.
Found in cerebrospinal fluid as the causative agent of cerebrospinal meningitis and in blood as the cause of septicemia (including
Waterhouse-Friderichsen syndrome), rarely in lower genital tract infections and pneumonia. Some strains may colonize the throat or
nasopharynx as normal flora.
May produce bacteriocins. Resistant to colistin.
It is a major cause of bacterial meningitis and septicemia worldwide. Certain types
N. meningitidis are usually associated with meningitis. Serogroups A, B, C, and
W-135 have most frequently been associated with epidemics. The ability to inflict
damage on its host is correlated with adherence to mucosal epithelial cells in the
nasopharynx and further invasion of subepithleial tissues and blood vessels.

Frequently found in a commensal state in the oro- or nasopharynx of asymptomatic
carriers. A presumptive diagnosis is suggested by finding Gram-negative diplococci
in cerebrospinal or synovial fluid or the aspirate from a petechial or purpuric lesion,
and not from a throat swab, nasopharyngeal aspirate, or conjunctival swab.
  1. Tone Tonjum, 2005. Order IV. Neisseriales ord. nov. In:  Bergey’s Manual of Systematic Bacteriology, Second edition, Vol two, part C
    The Alpha-, Beta-, Delta-, and Epsilonproteobacteria, George M. Garrity (Editor-in-Chief), pp 774-863.
  2. Daniel C. Stein, 2006. The Neisseria. In: The Prokaryotes Third Edition, Volume 5: Proteobacteria: Alpha and Beta Subclasses,
    Martin Dworkin (Editor-in-Chief), pp 602–647.
  3. Magnus Unemo (Editor-in-Chief), 2013. Laboratory diagnosis of sexually transmitted infections, including human immunodeficiency
    virus, pp 44-45. World Health Organization, ISBN 978 92 4 150584 0.
Positive results for catalase, oxidase, acid production from glucose and maltose.

Negative results for DN-ase, iodine test (polysaccharide synthesis), nitrate reduction, tributyrin hydrolysis, acid production from:
fructose, lactose, mannose and sucrose.

Nitrite is toxic to
N. meningitidis so that the reduction of nitrite is only observed at low concentration.
(c) Costin Stoica
Culture media
Biochemical tests
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