Laboratory diagnosis of adult Gonorrhea (Neisseria)

In this article, we are going to discuss the laboratory procedures required to diagnose Neisseria  Gonorrhoea ,the causative organism of Gonorrhea  which is one of the known sexually-transmitted diseases (STDs) allover the world .
A. Specimens 
The specimens can be obtained from urethral discharge in male , and from urethral and cervical discharge in addition to Rectal swabs in female .

B. Direct detection 
1. Gram-stained smears : show intra-cellular, Gram-negative diplococci inside some PMNs .
- Smears of urethral discharge from men with symptomatic gonococcal urethritis are highly sensitive and sufficient for diagnosis of male Acute Gonorrhoea .
- Smears of females or chronic males are less sensitive since the small number of gonococci maybe overlooked by the predominant microbial flora.Cultivation is necessary to reach a diagnosis .

2. Direct detection of gonococcal antigen in specimens by ELISA .

3. A nucleic acid probe test can detect gonococcal nucleic acid in specimens .

4. Nucleic acid amplification tests : Ligase chain reaction (LCR) or PCR .

- One of those methods allows a level of diagnosis adequate to initiate Antimicrobial therapy and sufficient for people at high risk of gonorrhea .
- When there are sociologic or medicolegal  implications , a definitive diagnosis is essential .This diagnosis can only be made by culture and identification of the viable organism as follows :

C. Cultivation 
- The specimens are plated onto chocolate agar and modified Thayer-Martin medium (MTM)
- Cultures should be incubated in a humid atmosphere with 5-10 % CO2 at 37'C .

D. Identification
- After incubation for 1-3 days , colonies should be examined for morphology and Gram stain and Oxidase test .
- Colonies showing Gram-negative diplococci and oxidase positive are considered Neisseria .
- Neisseria  Gonorrhoeae produces acid from Glucose ,, its antigens can be identified by agglutination of fluorescent antibody test .
- It can also be identified by one of the molecular methods e.g Nucleic acid probe, LCR or PCR .

E. Serology 
Detection of gonococcal antibodies in patients' sera is not useful .
Read Also : 
Gonorrhoea causes , symptoms , prevention and treatment with video
Laboratory diagnosis of adult Gonorrhea (Neisseria)
Dr.Tamer Mobarak


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