Neisseria gonorrhoeae- Morphology, Cultural characteristics, Biochemical Properties

 Neisseria is the only pathogenic Gram negative diplococci 

Two species of Neisseria causes disease in humans; Neisseria meningitidis and Neisseria gonorrhoeae.

 

Neisseria gonorrhoeae (Gonococcus) causes the venereal disease gonorrhoea, the second most common sexually transmitted disease (STDs) of worldwide importance (Chlamydial infections are more common).

 

Human beings are only known hosts of N. gonorrhoeae - It causes natural infection only in humans.

 

Cause an acute, infectious, sexually transmitted disease of the mucous membranes of the genitourinary tract, eye, rectum, and throat - gonorrhea, neonatal conjunctivitis (ophthalmia neonatorum) and pelvic inflammatory disease (PID).

 

Neisseria gonorrhoeae thrives in a CO₂ environment, therefore, the urethra, cervix, rectum, and throat are the main sites of infection.

 

 Gonococcus was first described in gonorrheal pus by Neisser in 1879.

Bumm in 1885 cultured the coccus & proved its pathogenicity by inoculating human volunteers.

 

Morphology:

·         Gram-negative, oxidase-positive, diplococcus (seen in pairs) – typically kidney shaped -adjacent sides concave-

·         In urethral discharge it is predominately found within the polymorphs - Intracellular - Some cells may contain as many as 100 cocci.

Urethral exudate containing Neisseria gonorrhoeae from a patient with gonococcal urethritis -typical intracellular gram-negative diplococci, and extracellular gram-negative organisms, which is diagnostic for gonococcal urethritis.

·         Nonmotile

·         Non-capsulated

·         Have pili- facilitate adhesion of the cocci to mucosal surface & promote virulence 

 

Cultural characteristics

• ·         More difficult to grow
• ·         Aerobic -may grow anaerobically also
• ·         Growth occurring best at pH 7.2 – 7.6 
• ·         Optimum temperature for growth – 35 - 36⁰ C; no growth if the temperature is less than 25⁰C or more than 38.5⁰C
• ·         Growth is good in presence of 5 -10 % CO₂
• ·         Grow well on enriched media like Chocolate Agar
• ·         Selective medium – THAYER – MARTIN medium (contains Vancomycin + Colistin + Nystatin which inhibit most of the contaminants like nonpathogenic Neisseria).
• ·         Small, round, translucent, convex or slightly umbonate with finely granular surface and lobate margins.
• ·         Soft and easily emulsifiable

 

                                                                Thayer-Martin agar

Biochemical

• ·         Oxidase positive (prompt positive reaction)
• ·         Catalase positive
• ·         Glucose  utilized with acid production, but not maltose, sucrose/lactose
• ·         Indole  not produced
• ·         Nitrates not reduced

 

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