Neisseria gonorrhoeae (gonococcus)
Neisseria gonorrhoeae on a selective medium for pathogenic Neisseria species after 48 hours of cultivation. Gonococci are the most fastidious of the Neisseria species, require complex growth media and are highly susceptible to toxic substnces (e.g., fatty acids). This sheep blood agar medium is supplemented with vitamins (vitamin B1, vitamin B12, para-aminobenzoic acid (intermediate in the synthesis of folate by bacteria), coenzymes (NAD), amino acids (glutamine, cysteine, cystine), nucleobases (adenine, guanine) and minerals essential for growth.
Media for N.gonorrhoeae contain antimicrobials that inhibit the growth of organisms other than N. gonorrhoeae; typically vancomycin (inhibits gram-positive bacteria), colistin (inhibits gram-negative bacteria including the commensal Neisseria spp.), trimethoprim (inhibits swarming of Proteus spp.) and nystatin or amphotericin B (antifungal agents). Gonococci are not able to grow on common blood agar. Often are used media resembling chocolate agar in appearance(e.g., modified Thayer-Martin agar(MTM) or Martin-Lewis agar(ML).
Plates are always incubated in a CO2-enriched, humid atmosphere (some gonococci require CO2 for growth, the growth of all species is enhanced by carbon dioxide). Colonies of N.gonorrhoeae vary in diameter from 1 to 4.0 mm after 48 hours owing to the formation of different colony types (designated T1, T2, T3, T4). The colonies are smooth and nonpigmented. Some strains may produce atypical small colonies.
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 disease gonorrhea. 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 (gonorrhoea) and is transmitted via sexual contact.
Neisseria is usually isolated on Thayer-Martin agar - an agar plate with three different antibiotics and nutrients which not only facilitate the growth of Neisseria species, but inhibit the growth of gram-positive organisms and most bacilli and fungi. Further testing to differentiate the species includes testing for oxidase (all 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.
Symptoms of infection with N. gonorrhoeae differ depending on the site of infection. Infection of the genitals can result in a purulent (or pus-like) discharge from the genitals which may be foul smelling, inflammation, redness, swelling, dysuria and a burning sensation during urination. N. gonorrhoeae can also cause conjunctivitis, pharyngitis, proctitis or urethritis, prostatitis and orchitis. Conjunctivitis is common in neonates. Neonatal gonorrheal conjunctivitis is contracted when the infant is exposed to N. gonorrhoeae in the birth canal, and can result in corneal scarring or perforation. 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 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).
Neisseria gonorrhoeae basic characteristics
- GRAM-NEGATIVE DIPLOCOCCI
- CATALASE: POSITIVE
- OXIDASE: POSITIVE
Identification of Neisseria gonorrhoeae
- Doesn't grow on common blood agar
- Acid production from glucose
- No acid production from maltose
- No acid production from lactose
- No acid production from sucrose
- ONPG negative
Antibiotic treatment of Neisseria gonorrhoeae
Should be always guided by in vitro susceptibility tests!!
Fluoroquinolones (e.g., ciprofloxacin) are not recommended as empiric treatment for gonococcal infections in many parts of the world!!
- cefixime (plus azithromycin or doxycycline if chlamydia not ruled out)
- ceftriaxone (plus azithromycin or doxycycline if chlamydia not ruled out)
- spectinomycin (plus azithromycin or doxycycline if chlamydia not ruled out)
- cefotaxime (plus azithromycin or doxycycline if chlamydia not ruled out)
- cefoxitin (plus azithromycin or doxycycline if chlamydia not ruled out)
Neisseria gonorrhoeae on agar plates
Neisseria gonorrhoeae identification
Neisseria gonorrhoeae micrographs
CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC)
- Gonorrhea - CDC Fact Sheet
- Gonorrhea Laboratory Information
- Identification of N. gonorrhoeae
- Acid Detection Test