The genus Neisseria are group of bacteria which causes human diseases.
Neisseria meningitidis (N. meningitidis/ meningococcus) and Neisseria gonorrhoeae (N. gonorrhoeae/ gonococcus) are the two important human pathogens.
Neisseria meningitidis and Neisseria gonorrhoeae show very similar morphological characteristics in culture as well as in gram stain.
They are gram negative oval shape cocci.
Usually, they are occurring in pairs and joining sides are flattened (bean shaped appearance).
N. meningitidis mainly responsible for meningitis and meningococcemia.
Infections caused by N. meningitidis are the major cause of children deaths in some countries, especially in America.
N. gonorrhoeae causes the disease gonorrhea.
It is a sexually transmitted disease.
It also causes diseases like pelvic inflammatory disease (PID) and neonatal conjunctivitis (ophthalmia neonatorum).
From the pus containing exudates such as cerebrospinal fluid (CSF) or urethral discharge, many gram-negative diplococci can be found within polymorphonuclear cells (intra cellular organisms).
Gonococcus are mainly found than meningococcus.
Extracellular cocci also can be occurred.
However, variations in the size and intensity of staining can be seen.
Most of the other members of genus Neisseria are commensals of upper respiratory tract.
They cause diseases occasionally in immuno-suppressed patients.
They are N. lactamica, N. cinerea, N. subflava, N. sicca, N. polysaccharea, N. mucosa and N. flavescens and Several other commensal organisms.
For the diagnosis of Neisseria species, specimens such as cerebrospinal fluid, blood for culture, swabs from skin lesions, urethral exudate, cervical exudate, centrifuged urine from male patients, rectal swabs when indicated, eye swabs specially from neonates are collected.
Microscopy
Neisseria are non-motile organisms. Some are capsulated and some are non-capsulated.
In gram-stained slides prepared directly from the specimens, Gram negative diplococcus can be seen in pus cells (intracellular organisms).
When in preparation of direct smears, it is necessary to avoid damaging of pus cells.
In the smears prepared from cultures, they appear as Gram negative cocci.
Culture
Neisseria are aerobes or facultative anaerobes.
Normally commensal (Non-pathogenic) Neisseria grow on ordinary prepared nutrient agar media.
However, pathogenic Neisseria (meningococci and gonococci) require additional nutrients like heated blood (chocolate agar) for their growth.
Cultures are incubated in 5–10% carbon dioxide and at 35°C- 37°C in moist atmosphere. Growth is slow.
As these organisms are fastidious, it is necessary to culture them with minimum delay.
On chocolate agar
Glistening, grey color colonies can be seen.
They are slightly convex and measures 0.5- 1.0 mm in diameter after incubation about 18 – 24 hours.
Colonies get much larger when they incubated more than 24 hours.
In Gonococcus after incubate more than 24 hours, they give crenated margins and slightly rough edges.
Modified New York City (MNYC) medium, Thayer Martin medium and Robertson’s cooked meat medium are also used along with the chocolate agar according to the site of specimen and clinical features.
Biochemical Identification
Pathogenic Neisseria are rapidly oxidase positive.
However, non-pathogenic Neisseria react very slowly with oxidase reagent.
For the identification of Neisseria to species level, it is necessary to perform carbohydrate utilization reactions.
In carbohydrate utilization reactions N. gonorrhoeae produces acid only from glucose.
But N. meningitidis produces acid from both glucose and maltose.
Enzyme detection tests are also useful for the identification of Neisseria.
Commercially available kits are used for the rapid detection of pre- formed enzymes such as aminopeptidases and β-galactosidase
Gene sequencing is also useful for the further confirmation of this organism.
Treatment
According to the infection, antibiotics use to treat are different.
Penicillin G, Ceftriaxone, Doxycycline, Cefoxitin, Spectinomycin, Ciprofloxacin, Azithromycin.
Prevention
Chemoprophylaxis, and Vaccination (immunization) is the best method of controlling meningococcal infection.
For the prevention of gonococcal infection, usage of condoms, treatment of patients with symptoms as well as their contacts is necessary.
No vaccine is available for the prevention of gonococcal infection.Â
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