Cocci 0.6–1.9 µm in diameter, occurring singly but often in pairs with adjacent sides flattened; two species (Neisseria elongata and N. weaveri) are exceptions and consist of short rods 0.5 µm wide, often arranged as diplobacilli or in chains. Division of the coccal species is in two planes at right angles to each other, sometimes resulting in tetrads. Capsules and fimbriae (pili) may be present. Endospores are not present. Gram negative, but there is a tendency to resist decolorization. Swimming motility does not occur and flagella are absent. Aerobic. Some species produce a yellow carotenoid pigment. Some species are nutritionally fastidious and hemolytic. Optimal temperature, 35–37°C. Oxidase positive. Catalase positive except most strains of N. elongata. Carbonic anhydrase is produced by all species. All species reduce nitrite except N. gonorrhoeae and N. canis. Neisseria spp. produce acid from carbohydrates by oxidation, not fermentation. Chemoorganotrophic. Exotoxins are not produced. Some species are saccharolytic. Inhabitants of the mucous membranes of mammals. Some species are primary pathogens of humans. The genus Neisseria belongs to the family Neisseriaceae of the Betaproteobacteria.The mol% G + C of the DNA is: 48–56.Type species: Neisseria gonorrhoeae
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]
Microbial Abundance Data: Neisseria (Percent of total population with standard deviation [PMID: 22698087])
