Neisseria gonorrhoeae
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Direct answer
Neisseria gonorrhoeae is a Gram-negative, oxidase-positive diplococcus that causes urethritis, cervicitis and pelvic inflammatory disease. In urethral discharge from men it appears as intracellular diplococci within neutrophils, a finding that is highly specific when symptoms are present. Its ability to acquire resistance to penicillin, tetracycline, fluoroquinolones and reduced cephalosporin susceptibility now shapes treatment choices.
What you must remember
- Gram stain: Gram-negative diplococci within neutrophils in urethral discharge from men, but the sensitivity is much lower in cervical or pharyngeal samples from women.
- Isolation: grows on Thayer-Martin medium, a chocolate-based selective agar containing vancomycin, colistin and nystatin, often with trimethoprim, incubated in carbon dioxide.
- Biochemistry: oxidase positive, ferments glucose only and does not ferment maltose, which separates it from Neisseria meningitidis.
- Pelvic inflammatory disease: the main female complication, causing tubal scarring, infertility and ectopic pregnancy.
- Disseminated infection: an arthritis-dermatitis syndrome with tenosynovitis, skin pustules and migratory polyarthralgia, with septic arthritis of a large joint in some patients.
- Fitz-Hugh-Curtis syndrome: perihepatitis with right upper quadrant pain from adhesions between the liver capsule and peritoneum.
- Ophthalmia neonatorum: purulent conjunctivitis in the newborn, acquired in the birth canal, which can perforate the cornea if untreated.
Mechanisms of resistance in the laboratory
Gonococcal resistance arises through plasmid acquisition and chromosomal mutation, and each mechanism affects a different drug class. The table below groups the common mechanisms by the marker that a laboratory can detect.
| Mechanism | Drugs affected | Laboratory marker |
|---|---|---|
| Plasmid penicillinase (PPNG) | Penicillin, ampicillin | Beta-lactamase test positive |
| Chromosomal gyrA mutation | Ciprofloxacin | Raised ciprofloxacin MIC |
| Mosaic penA allele (altered PBP2) | Cephalosporins, including cefixime | Raised cephalosporin MIC |
| Tetracycline resistance (tetM) | Tetracycline, doxycycline | Tetracycline MIC raised |
Each mechanism reduces a different class, so the resistance pattern in a region guides empirical therapy. WHO-based syndromic guidance in India pairs ceftriaxone with azithromycin, because single-drug failures have been reported and azithromycin also covers Chlamydia trachomatis; some Western guidelines now use ceftriaxone alone, so check the latest NACO document.
Treatment is then reviewed against local surveillance data and the isolate's susceptibility results. Reporting the MIC rather than a simple sensitive or resistant label lets clinicians see creeping resistance before treatment failure occurs. Test of cure after treatment is advised when culture is the basis of diagnosis, since resistance may be missed by empirical therapy alone.
Where the exam tries to catch you
Gonorrhoea questions reward precision about the specimen, the medium and the complication.
- Trap: reading a negative urethral Gram stain as excluding gonorrhoea in a woman Correct: the cervical Gram stain is far less sensitive, so nucleic acid amplification testing is preferred for women.
- Trap: expecting gonococci to grow on MacConkey agar Correct: they are fastidious and need enriched chocolate media such as Thayer-Martin medium.
- Trap: dismissing newborn conjunctivitis as a minor infection Correct: gonococcal ophthalmia neonatorum can perforate the cornea quickly and needs urgent treatment.
Frequently asked questions
Which medium is used to isolate Neisseria gonorrhoeae?
Thayer-Martin medium, a chocolate-based selective agar containing vancomycin, colistin and nystatin, is used to isolate Neisseria gonorrhoeae. It is incubated in carbon dioxide, because gonococci are fastidious and do not grow on ordinary media.
Why is pelvic inflammatory disease important in gonorrhoea?
Pelvic inflammatory disease is the most important female complication of Neisseria gonorrhoeae, because it causes tubal scarring. Tubal damage raises the risk of infertility and ectopic pregnancy, so early treatment of cervicitis is a priority.
What is Fitz-Hugh-Curtis syndrome in gonorrhoea?
Fitz-Hugh-Curtis syndrome is perihepatitis with right upper quadrant pain, caused by inflammatory adhesions between the liver capsule and the peritoneum. It is a recognised complication of pelvic inflammatory disease caused by Neisseria gonorrhoeae or Chlamydia trachomatis.
How does drug resistance affect empirical gonorrhoea treatment?
Resistance to ciprofloxacin is widespread, and reduced cephalosporin susceptibility has been reported, so single-drug therapy is no longer relied upon. Indian syndromic guidance pairs ceftriaxone with azithromycin, adjusted to local resistance surveillance and the latest NACO document.
Why is prophylaxis given to newborns against gonococcal eye infection?
Prophylaxis is given to newborns because Neisseria gonorrhoeae in the birth canal can cause severe purulent conjunctivitis within days of birth. Untreated ophthalmia neonatorum can damage the cornea and lead to blindness, so prevention at birth is essential.