出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/05/30 18:16:25」(JST)
| Neisseria gonorrhoeae | |
|---|---|
| Neisseria gonorrhoeae cultured on two different media types and presented in stereoscopic 3d. | |
| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Beta Proteobacteria |
| Order: | Neisseriales |
| Family: | Neisseriaceae |
| Genus: | Neisseria |
| Species: | N. gonorrhoeae |
| Binomial name | |
| Neisseria gonorrhoeae Zopf, 1885 |
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| Synonyms | |
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Gonococcus Neisser 1879 |
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Neisseria gonorrhoeae, also known as gonococci (plural), or gonococcus (singular), is a species of Gram-negative coffee bean-shaped diplococci bacteria responsible for the sexually transmitted infection gonorrhea.[1]
N. gonorrhoea was first described by Albert Neisser in 1879.
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Neisseria are fastidious Gram-negative cocci that require nutrient supplementation to grow in laboratory cultures. Specifically, they grow on chocolate agar with carbon dioxide. These cocci are facultatively intracellular and typically appear in pairs (diplococci), in the shape of coffee beans. Of the eleven species of Neisseria that colonize humans, only two are pathogens. N. gonorrhoeae is the causative agent of gonorrhea (also called "The Clap," which is derived from the French word "clapier," meaning "brothel") and is transmitted via sexual contact.[2]
Neisseria is usually isolated on Thayer-Martin agar—an agar plate containing antibiotics (Vancomycin, Colistin, Nystatin, and SXT) and nutrients that facilitate the growth of Neisseria species while inhibiting the growth of contaminating bacteria and fungi.Further testing to differentiate the species includes testing for oxidase (all clinically relevant Neisseria show a positive reaction) and the carbohydrates maltose, sucrose, and glucose test in which N. gonorrhoeae will only oxidize (that is, utilize) the glucose.
N. gonorrhoeae are motile (twitching motility) and possess type IV pili to adhere to surfaces. The type IV pili operate mechanistically similar to a grappling hook. Pili extend and attach to a substrate which signals the pilus to retract, dragging the cell forward. N. gonorrhoeae are able to pull 100,000 times their own weight and it has been claimed that the pili used to do so are the strongest biological motor known to date, exerting one nanonewton.[3]
N. gonorrhoeae has surface proteins called Opa proteins, which bind to receptors on immune cells. In so doing, N. gonorrhoeae is able to prevent an immune response. The host is also unable to develop an immunological memory against N. gonorrhoeae – which means that future reinfection is possible. N. gonorrhoeae can also evade the immune system through a process called antigenic variation, in which the N. gonorrhoeae bacterium is able to alter the Opa proteins that adorn its surface. The many permutations of surface proteins make it more difficult for immune cells to recognize N. gonorrhoeae and mount a defense.[4]
N. gonorrhoeae is naturally competent for DNA transformation as well as being capable of conjugation. Both of these concepts allow for the DNA of N. gonorrhoeae the ability to undergo conformational changes. Especially dangerous to the health industry is the ability to conjugate since this can lead to antibiotic resistance.
In 2011, researchers at Northwestern University found evidence of a human DNA fragment in a Neisseria gonorrhoeae genome, the first example of horizontal gene transfer from humans to a bacterial pathogen.[5][6]
Symptoms of infection with N. gonorrhoeae differ depending on the site of infection. Note also that 10% of infected males and 80% of infected females are asymptomatic.[citation needed]
Infection of the genitals can result in a purulent (or pus-like) discharge from the genitals which may be foul smelling. Symptoms may include inflammation, redness, swelling, and dysuria
N. gonorrhoeae can also cause conjunctivitis, pharyngitis, proctitis or urethritis, prostatitis and orchitis.
Conjunctivitis is common in neonates (newborns), and silver nitrate or antibiotics are often applied to their eyes as a preventive measure against gonorrhoea. Neonatal gonorrheal conjunctivitis is contracted when the infant is exposed to N. gonorrhoeae in the birth canal and can lead to corneal scarring or perforation, resulting in blindness in the neonate.
Disseminated N. gonorrhoeae infections can occur, resulting in endocarditis, meningitis or gonococcal dermatitis-arthritis syndrome. Dermatitis-arthritis syndrome presents with arthralgia, tenosynovitis and painless non-pruritic (non-itchy) dermatitis.
Infection of the genitals in females with N. gonorrhoeae can result in pelvic inflammatory disease if left untreated, which can result in infertility. Pelvic inflammatory disease results if N. gonorrhoeae travels into the pelvic peritoneum (via the cervix, endometrium and fallopian tubes). Infertility is caused by inflammation and scarring of the fallopian tube. Infertility is a risk to 10 to 20% of the females infected with N. gonorrhoeae.
If N. gonorrhoeae is resistant to the penicillin family of antibiotics, then ceftriaxone (a third-generation cephalosporin) is often used. Sexual partners should also be notified and treated. [7]
Antibiotic-resistant gonorrhea has been noted by epidemiologists; beginning in the 1940s gonorrhea was treated with penicillin, but doses had to be continually increased in order to remain effective, and by the ’70s, penicillin- and tetracycline-resistant gonorrhea emerged in the Pacific Basin. These resistant strains then spread to Hawaii, California, the rest of the United States, and Europe. Fluoroquinolones were the next line of defense, but soon resistance to this antibiotic emerged as well. Since 2007, standard treatment has been third-generation cephalosporins, such as ceftriaxone, which are considered to be our “last line of defense.” Recently, a high-level ceftriaxone-resistant strain of gonorrhea, called H041, was discovered in Japan. Lab tests found it to be resistant to high concentrations of ceftriaxone, as well as most of the other antibiotics tested. Within N. gonorrhoeae, there are genes that confer resistance to every single antibiotic used to cure gonorrhea, but thus far they do not coexist within a single gonococcus. Because of N. gonorrhoeae’s high affinity for horizontal gene transfer, however, antibiotic-resistant gonorrhea is seen as an emerging public health threat.[8]
Patients should also be tested for other sexually transmitted infections, especially Chlamydia infections, since co-infection is frequent (up to 50% of cases). Antibacterial coverage is often included for Chlamydia because of this.
Transmission can be reduced by the usage of latex barriers, such as condoms or dental dams, during intercourse, oral and anal sex, and by limiting sexual partners.
Development of Neisserial vaccines has been challenging due to the nature of these organisms, in particular the heterogeneity, variability and/or poor immunogenicity of their outer surface components. As strictly human pathogens, they are highly adapted to the host environment but have evolved several mechanisms to remain adaptable to changing microenvironments and avoid elimination by the host immune system. Currently, serogroup A, C, Y and W-135 meningococcal infections can be prevented by vaccines. However there is no comprehensive serogroup B vaccine, and the prospect of developing a gonococcal vaccine in the near future is remote. Researchers have identified a bacterial protein that may be useful in creating a vaccine against Neisseria gonorrhoeae, the microbe responsible for the notorious sexually transmitted disease. A vaccine incorporating this protein protected against infection in mice. Gonorrhoeae has no capsule, so efforts to develop a vaccine have focused on targeting the bacterium’s surface proteins.[citation needed]
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| リンク元 | 「Neisseria gonorrhoeae」 |