Neisseria Gonorrhoeae Culture

Neisseria gonorrhoeae culture is indicated in the diagnosis of N gonorrhoeae infection. N gonorrhoeae causes the sexually transmitted disease gonorrhea, among other diseases.

N gonorrhoeae culture results in uninfected persons are negative, meaning no growth. ^{[1, 2]}

Gonococci are not normal inhabitants of the respiratory or genital flora.

Positive culture indicates active infection with N gonorrhoeae.

In men, the best specimen for N gonorrhoeae culture is urethral exudate or urethral scrapings (obtained with a loop or special swab). Throat or rectal cultures in men are needed only when indicated by sexual practices.

In women, cervical swabs are preferred over urethral or vaginal specimens. The combination of a cervical and an anal canal culture return the highest diagnostic yield in women, since some patients with rectal gonorrhea have negative cervical culture results.

Swabs may be streaked directly onto culture media or promptly transmitted (in < 4 hours) to a laboratory in a suitable transport medium. Laboratory requests must specify the suspicion of gonorrhea so that media that satisfy the nutritional requirements of the gonococcus and inhibit competing normal flora can be seeded.

The selective medium (eg, Martin–Lewis agar) is an enriched selective chocolate agar with antibiotics. The exact formulation has changed over the years but includes agents active against gram-positive bacteria (vancomycin), gram-negative bacteria (colistin, trimethoprim), and fungi (nystatin, anisomycin) at concentrations that do not inhibit N gonorrhoeae.

Colonies appear after 1-2 days of incubation in carbon dioxide at 35°C. They may be identified as Neisseria by demonstration of typical Gram stain morphology and a positive oxidase test result.

Description

Gonorrhea is a common N gonorrhoeae infection that is transmitted almost exclusively by sexual contact or perinatally and primarily affects the mucous membranes of the urethra and cervix and, less frequently, those of the rectum, oropharynx, and conjunctivae.

Ascending genital infection in women leads to endometritis and salpingitis —collectively called pelvic inflammatory disease (PID), the predominant complication and one of the most common causes of female infertility.

Other manifestations of N gonorrhoeae infection include acute epididymitis; ophthalmitis; disseminated infection with arthritis, dermatitis, and sometimes endocarditis; and transmission to the neonate with attendant conjunctivitis (ophthalmia neonatorum).

Indications/Applications

N gonorrhoeae culture is indicated in the diagnosis of N gonorrhoeae infection. N gonorrhoeae causes the sexually transmitted disease gonorrhea, among other diseases.

Considerations

Attention to detail is necessary for isolation of the gonococcus because it is a fragile organism that is often mixed with hardier members of the normal flora. Success requires proper selection of culture sites, protection of specimens from environmental exposure, culture on appropriate media, and definitive laboratory identification.

A study by Nash et al indicated that with regard to N gonorrhoeae culture recovery in patients who had a positive nucleic acid amplification test (NAAT), the best culture recovery rate was associated with urethral infection (91%). Endocervical (61.2%), vaginal (47.4%), rectal (39.8%), and pharyngeal (27.7%) infections came next. Collection time also influenced culture recovery, which was greatest for specimens collected on the same day as NAAT specimens were, as opposed to later. Moreover, symptoms showed an association with culture recovery when specimens were collected at urethral and rectal infection sites. ^[3]