Neisseria gonorrhoeae (Gonococci)

It is the causative organism of gonorrhoea and ophthalmia neonatorum.

Morphology

Like meningococci, gonococci are gram negative diplococci present intracellularly but unlike meningococci , gonococci are non capsulated. The endotoxin of gonococci is lipooligosaccharide which is slightly different from other gram negative bacteria which have lipopolysaccharide.

Classification

They can be typed into more than 100 serotypes based on their pilus protein.

Human Pathology

Gonococci cause gonorrhoea and ophthalmia neonatorum. Gonorrhoea presents with purulent urethral discharge and dysuria in men. It may also cause epididymitis and proctitis. In women it causes PID (pelvic inflammatory disease) which may lead to infertility and ectopic pregnancy from tubal scarring. Disseminated gonococcal infection presents with septic arthritis, tenosynovitis, skin pustules, endocarditis and meningitis.

Pili and outer membrane protein are important in initial attachment to the host cell. Non piliated gonococci are avirulent.

Prophylactic erythromycin applied topically to the eye is given to all newborns at birth.

Laboratory diagnosis of Gonococcal infections

In men gram stain of urethral discharge showing typical gonococcal morphology is good enough for diagnosis while in women gram stain must be followed by culture to confirm the diagnosis. The sensitivity and specificity for urethral smears is 90% to 95%, respectively, versus 60% sensitivity and over 90% specificity for endocervical smears.

Culture medium should be chosen depending on the site of specimen. Sterile sites like blood can be cultured on chocolate agar while non sterile sites like urethral discharge are cultured on selective media like Thayer Martin , Martin Lewis or New York city medium which is chocolate agar to which antibiotics vancomycin, colistin, trimethoprim and nystatin or amphotericin B have been added.

Gonococci are catalase positive, oxidase positive, ferment glucose but not maltose. Fluorescent antibody tests with antibodies binding to outer membrane proteins porins IA and IB can be done to confirm a culture as gonococcus. Similarly coagglutination tests can be used. Rapid, highly sensitive and specific nucleic acid tests can be done on urine and vaginal swabs.