Neisseria cinerea
Neisseria cinerea is a commensal species grouped with the Gram-negative, oxidase-positive, and catalase-positive diplococci. It was first classified as "Micrococcus cinereus" by Alexander von Lingelsheim in 1906. Using DNA hybridization, "N. cinerea" exhibits 50% similarity to "Neisseria gonorrhoeae". Classification. "Neisseria cinerea" has been formerly classified as many other organisms, including "Moraxella catarrhalis" and "Neisseria pseudocatarrhalis". It is often mistaken for "N. gonorrhoeae" with which it shares morphological and biochemical traits. Both are isolated from similar infections, including endocervical and rectal infections, neonatal conjunctivitis, and lymphadenitis."N. cinerea" has even been isolated on gonococcal selective media  specifically made to isolate "N. gonorrhoeae". Colony morphology. One important difference between "N. cinerea" and "N. gonorrhoeae" is that "N. cinerea" is slightly more pigmented and exhibits a golden-brown rather than a pinkish-brown pigmentation. The average diameter of "N. cinerea" colonies varies, but stays around 1–2 mm. The colonies are convex, translucent, and glistening. No change occurs in the color of the media used to isolate "N. cinerea" before or after staining with Lugol's iodine. Biochemical processes. "Neisseria cinerea" can produce acid from glucose like "N. gonorrhoeae", but it will then oxidize the acid to carbon dioxide . Although it can break down glucose, it is unable to use glucose or other carbohydrates for energy, making it asaccharolytic. In addition, "N. cinerea" will react in coagglutination serologic tests and, like "N. gonorrhoeae", it produces the enzyme hydroxyprolylaminopeptidase."N. cinerea" does not reduce nitrate, but it does reduce nitrite. Proline, arginine, cystine, and cysteine are required for its growth. "N. cinerea" does not react with antigonococcal protein I monoclonal antibodies and does not produce immunoglobulin A protease, unlike "N. gonorrhoeae". Also unlike "N. gonorrhoeae", "N. cinerea" is not resistant to the antibiotic colistin, and it can grow on Mueller –Hinton agar and trypticase soy agar. Disease. "Neisseria cinerea" is classified as a nonpathogenic bacterium, but has been isolated from numerous infections including acute meningitis. Many studies indicate that "N. cinerea" colonizes the oropharynx and sometimes the genital tract. A few infections which could possibly be caused by "N. cinerea" have been reported. However, in each case, the organism was misidentified as "N. flavescens", "N. gonorrhoeae", or "M. catarrhalis".