Neisseria gonorrhoeae: Disease, Pathogenesis and Laboratory Diagnosis

Neisseria gonorrhoeae (Gram negative diplococci)

Neisseria is the only pathogenic gram negative cocci (precisely diplococci). Two species of Neisseria causes disease in humans; Neisseria meningitidis and Neisseria gonorrhoeae.

Human beings are only known hosts of N.gonorrhoeae. Neisseria gonorrhoeae (often called gonococcus) causes gonorrhoea, the second most common sexually transmitted disease (STDs) of worldwide importance (Chlamydial infections are more common). It causes disease only in humans.

Morphology:

  1. Gram Negative cocci, usually seen in pairs (diplococci) with the adjacent sides flattened (typically kidney shaped); (Looks like 2 coffee beans kissing).
  2. In urethral discharge it is predominately found within the polymorphs.
Neisseria gonorrhoeae (Gram negative diplococci)
Neisseria gonorrhoeae (Gram negative diplococci)
  • Sensitive to dehydration and cold conditions.
  • Gonococci do not contain capsules (Meningococci does).

Mode of transmission

  1. Neonates acquired Neisseria gonorrhoeae from mother during passage through the birth canal. In newborn infants, Neisseria gonorrhoeae causes Ophthalmia neonatorum (purulent conjunctivitis).
  2. Sexual transmission: Acquired during unprotected sex with infected partner.

Virulence factors expressed by Neisseria gonorrhoeae

  1. Pili: Pili mediate attachment to mucosal cell surfaces and also are antiphagocytic. Piliated gonococci are usually virulent, whereas nonpiliated strains are avirulent.
  2. Lipooligosaccharides (LOS)
  3. Outer membrane proteins and Opa proteins eg. Porin A: Mediates invasion of the epithelial cells.
  4. IgA protease: It hydrolyze secretory IgA, which could otherwise block attachment to the mucosa.

Host defense against Neisseria gonorrhoeae

  1. Antibodies (Mainly IgA and IgG)
  2. Complement
  3. Neutrophils

Disease caused by Neisseria gonorrhoeae:

Gonococci causes both localized infections, usually in the genital tract, and disseminated infections.

  1. Gonorrhoea in men is characterized primarily by urethritis accompanied by dysuria and a purulent discharge. Epididymitis can occur.
  2. In women, infection is located primarily in the endocervix, causing a purulent vaginal discharge and intermenustrual bleeding (cervicitis). The most frequent complication in women is an ascending infection of the uterine tubes (salphingitis, Pelvic Inflammatory Disease), which can result in sterility or ectopic pregnancy as a result of scarring of tissues.

    Opthalmia neonatorum
    Opthalmia neonatorum
  3. In newly born children: Ophthalmia neonatorum (An eye infection which may develop within 2/3 days of vaginal delivery, affects cornea and can cause blindness)

Disseminated gonococcal infections occurs via the blood stream. Gonococcal strains causing disseminated infections are usually resistant to serum and complement. Disseminated infections commonly manifest as septic arthritis, tenosynovitis, pustules in the skin, endocarditis, and meningitis.

Laboratory diagnosis of Gonorrhoea

Algorithm for culture and identification of Neisseria gonorrhoeae
Algorithm for culture and identification of Neisseria gonorrhoeae

Sample: Urethral/Cervical/Vaginal discharge

  • To obtain a urethral specimen swab ( cotton or rayon swab) is inserted approximately 2cm in urethra and rotated gently before withdrawing.
  • If there is profuse urethral discharge in male, it can be collected without inserting the swab.
  • A few drops of first voided urine can be used in males, but the sensitivity is low compared to discharge.

Transport: Swabs collected for isolation of gonococci may be transported to the laboratory in modified Staurt’s or Amie’s charcoal transport media and held at room temperature until inoculated to culture media. Good recovery of gonococci is possible if swabs are cultured within 12 hours of collection.

Gram Staining 

neisseria gonorrhoea on MNC
Neisseria gonorrhoeae in New York City Agar (LCAT).

For men, a gram-stained smear of urethral discharge (exudate) showing intracellular Gram-negative diplococci is diagnostic. But as women may carry normal vaginal flora such as Veillonella or occasional gram-negative coccobacilli , may resemble gonococci, same results in case of women may not be diagnostic so culture and identification process is needed, which is a confirmatory test.

Culture 

Modified Thayer Martin Medium {Chocolate agar containing antibiotics (vancomycin, colistin, trimethoprim, and nystatin)} is most often used.  Modified Newyork City Medium (MNC)  is also used for the culture of Neisseria gonorrhoeae. MNC also supports the growth of Mycoplasma.

Biochemical tests for Neisseria gonorrhoeae identification

  1. Oxidase Test: Positive
  2. Ferments glucose but not maltose, sucrose or lactose
  3. DNase Test: Negative
  4. Beta-galactosidase (ONPG) Test: Negative
  5. Glutamyl-aminopeptidase (GAP) Test: Negative

Serology: Serological tests to determine the presence of antibody to gonococci are not useful for diagnosis.

Molecular Diagnosis: Presence of gonococcal nucleic acids in patient specimens, using amplification or non-amplification method. These tests are highly sensitive and specific.

Drug Resistance

Antimicrobial resistance in Neisseria gonorrhoeae has been categorized by the CDC as an “urgent threat” .

Neisseria gonorrhoeae infections is an urgent Threat (CDC)

Currently, the CDC recommends an intramuscular shot of an extended-spectrum cephalosporin (ESC), ceftriaxone, plus one oral dose of azithromycin as an empirical  treatment for uncomplicated or pharyngeal gonococcal infections.

Penicillin cures Gonorrhea (Source)

TIMELINE OF RESISTANCE:

  1. 1935s: Antimicrobial treatment of gonorrhea started in 1935 after discover of sulfanilamide. Neisseria gonorrhoeae developed widespread resistance to sulfanilamide within the first ten years resulting in treatment failures.
  2. 1940s: Penicillin is used as a treatment of choice for gonorrhea. Penicillin remained effective for next few decades despite a continuous and insidious increase in MICs.
  3. 1976: End of era of penicillin with discovery and worldwide spread of Neisseria gonorrhoeae harboring plasmid-mediated beta-lactamases.
  4. 2010s: Alarming decrease in cefixime susceptibility reported from around the world.
  5. 2018s: Combination of azithromycin and ceftriaxone – has failed to treat the disease (report from BBC)

After start of standard double regimen for the treatment of N.gonorrhoeae infection, Azithromycin resistance among N. gonorrhoeae is on the rise. Reduced susceptibility to ceftriaxone and cefixime has also been reported. Till date, all patients are successfully treated as azithromycin is rarely used as a monotherapy for gonorrhea, and most azithromycin-resistant isolate are still susceptible to ceftriaxone. However,
as the organism continues to develop resistance to ceftriaxone, we might end up with isolates highly resistant to both agents in the near future.

Further Resources:

  1. Laboratory diagnosis of Neisseria gonorrhoeae in NCBI 
  2. Gonococcal Infections: CDC
  3. When the clap hits back: Antimicrobial Resistance Threats in Neisseria gonorrhoeae: ASM

 
About tankeshwar 363 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion, I am working as a Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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