gonococci

''Neisseria gonorrhoeae'', also known as ''gonococcus'' (singular), or ''gonococci'' (plural), is a species of Gram-negative diplococci bacteria isolated by Albert Neisser in 1879. It causes the sexually transmitted genitourinary infection gonorrhea as well as other forms of gonococcal disease including disseminated gonococcemia, septic arthritis, and gonococcal ophthalmia neonatorum.

It is oxidase positive and aerobic, and it survives phagocytosis and grows inside neutrophils. Culturing it requires carbon dioxide supplementation and enriched agar ( chocolate agar) with various antibiotics ( Thayer–Martin). It exhibits antigenic variation through genetic recombination of its pili and surface proteins that interact with the immune system.

Sexual transmission is through vaginal, anal, or oral sex. Sexual transmission may be prevented through the use of barrier protection. Perinatal transmission may occur during childbirth, and may be prevented by antibiotic treatment of the mother before birth and the application of antibiotic eye gel on the eyes of the newborn. After an episode of gonococcal infection, infected persons do not develop immunity to future infections. Reinfection is possible due to ''N. gonorrhoeae's'' ability to evade the immune system by varying its surface proteins.

''N. gonorrhoeae'' can cause infection of the genitals, throat, and eyes. Asymptomatic infection is common in males and females. Untreated infection may spread to the rest of the body (disseminated gonorrhea infection), especially the joints (septic arthritis). Untreated infection in women may cause pelvic inflammatory disease and possible infertility due to the resulting scarring. Diagnosis is through culture, Gram stain, or nucleic acid tests, such as polymerase chain reaction, of a urine sample, urethral swab, or cervical swab. Chlamydia co-testing and testing for other STIs is recommended due to high rates of co-infection.

Microbiology

'' Neisseria'' species are fastidious, Gram-negative cocci that require nutrient supplementation to grow in laboratory cultures. ''Neisseria'' spp. are facultatively intracellular and typically appear in pairs (diplococci), resembling the shape of coffee beans. ''Neisseria'' is non-spore-forming, capable of moving using twitching motility, and an obligate aerobe (requires oxygen to grow). Of the 11 species of ''Neisseria'' that colonize humans, only two are pathogens. ''N. gonorrhoeae'' is the causative agent of gonorrhea and ''N. meningitidis'' is one cause of bacterial meningitis.

Culture and identification

''N. gonorrhoeae'' is usually isolated on Thayer–Martin agar (or VPN) agar in an atmosphere enriched with 3-7% carbon dioxide. Thayer–Martin agar is a chocolate agar plate (heated blood agar) containing nutrients and antimicrobials (vancomycin, colistin, nystatin, and trimethoprim). This agar preparation facilitates the growth of ''Neisseria'' species while inhibiting the growth of contaminating bacteria and fungi. Martin Lewis and New York City agar are other types of selective chocolate agar commonly used for ''Neisseria'' growth. ''N. gonorrhoeae'' is oxidase positive (possessing cytochrome c oxidase) and catalase positive (able to convert hydrogen peroxide to oxygen). When incubated with the carbohydrates lactose, maltose, sucrose, and glucose, ''N. gonorrhoeae'' will oxidize only the glucose.

Surface molecules

On its surface, ''N. gonorrhoeae'' bears hair-like pili, surface proteins with various functions, and sugars called lipooligosaccharides. The pili mediate adherence, movement, and DNA exchange. The Opa proteins interact with the immune system, as do the porins. Lipooligosaccharide (LOS) is an endotoxin that provokes an immune response. All are antigenic and all exhibit antigenic variation (see below). The pili exhibit the most variation. The pili, Opa proteins, porins, and even the LOS have mechanisms to inhibit the immune response, making asymptomatic infection possible.

Dynamic polymeric protein filaments called type IV pili allow ''N. gonorrhoeae'' to adhere to and move along surfaces. To enter the host the bacteria uses the pili to adhere to and penetrate mucosal surfaces. The pili are a necessary virulence factor for ''N. gonorrhoeae''; without them, the bacterium is unable to cause infection. To move, individual bacteria use their pili like a grappling hook: first, they are extended from the cell surface and attach to a substrate. Subsequent pilus retraction drags the cell forward. The resulting movement is referred to as twitching motility. ''N. gonorrhoeae'' is able to pull 100,000 times its own weight, and the pili used to do so are amongst the strongest biological motors known to date, exerting one nanonewton. The PilF and PilT ATPase proteins are responsible for powering the extension and retraction of the type IV pilus, respectively. The adhesive functions of the gonococcal pilus play a role in microcolony