Microbiology Test

Test : Neisseria gonorrhoeae smear


Indications : N. gonorrhoeae is usually detected by growing them in cultures. In some instances, a smear is ordered to detect the presence of the causative bacteria.

A sample is collected from the urethra, cervix, vagina or rectum using a cotton-tipped swab and a smear is made by gently rolling the swab on the slide.

The micro slide is then stained using gram stain kits which are commercially available and then viewed under oil immersion(1000x magnification) lens in a microscope.

Physiology : The genus Neisseria comprises of two important human pathogens, N. gonorrhoeae and N. meningitidis. The former causes gonorrhea, a sexually transmitted disease with high prevalence and low mortality while the latter causes meningococcal meningitis which has low prevalence but high mortality.

Neisseria gonorrhoeae infections usually affect the mucous membranes of the endocervix and urethra in females and of the urethra in males. It may later on spread to other tissues.

Many healthy individuals may harbor Neisseria meningitidis in their upper respiratory tract, but Neisseria gonorrhoeae is always an acquired pathogen and is not a member of the normal flora.

Normal Range : Negative

Interpretation :

Normal
No Neisseria growth is seen

Abnormal
Under an oil immersion lens (1000x magnification) of the microscope the following can be observed -

• Gram-negative kidney-shaped diplococci in polymorphonuclear leukocytes of urethral samples from males
• Gram-negative kidney-shaped diplococci can be seen clearly in urethral smears (sensitivity and specificity is 90% to 95% ). The sensitivity and specificity is much lower in endocervical smears or rectal specimens. This is due to the presence of other Gram-negative coccobacilli.

A positive result in the smear test will have to be confirmed with a Neisseria culture test.

Sample : Urethral swab

Test Method : Gram stain

Related Tests : Chlamydia trachomatis, Gram stain, Neisseria gonorrhoeae culture

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