Neisseria: Meaning, Classification and Cultural Characteristics | Human Parasite

In this article we will discuss about Neisseria:- 1. Meaning of Neisseria 2. Classification of Neisseria 3. Cultural Characteristics 4. Viability 5. Antigenic Structure 6. Pathogenicity and Clinical Features 7. Laboratory Diagnosis: Specimens 8. Culture 9. Treatment 10. Prevention and Control 11. Non-Specific Urethritis.

Contents:

1. Meaning of Neisseria
2. Classification of Neisseria
3. Cultural Characteristics of Neisseria
4. Viability of Neisseria
5. Antigenic Structure of Neisseria
6. Pathogenicity and Clinical Features of Neisseria
7. Laboratory Diagnosis of Neisseria: Specimens
8. Culture
9. Treatment of Neisseria
10. Prevention and Control of Neisseria
11. Non-Specific Urethritis

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1. Meaning of Neisseria:

Neisseria is Gram-negative coccus arranged in pairs with long axes parallel and is strictly a human parasite. Neisseria gonorrhoeae (gonococcus) and N. meningitidis (meningococcus) are the two principal human pathogens.

2. Classification of Neisseria:

1. Pathogenic 1. N. gonorrhoeae – causes gonorrhoea Greek word gonos (reed) and rhoia (flow)

2. N. meningitidis – causes pyogenic meningitis, n.

Non-pathogenic (commensals)

N. pharyngitidis (includes N. flavo, N. sicca, N. perflava, N. subflava, and other species.

Neisseria Gonorrhoeae (Gonococcus):

It is a causal agent of gonorrhoea, a venereal disease. Morphology and Staining. N. gonorrhoeae are Gram-negative non-motile diplococci, about 0.8 p in diameter, and are intracellular—so pus cells are almost filled with gonococci (Fig. 26.1).

3. Cultural Characteristics of Neisseria:

They are aerobe and grow well at optimum temperature of 37°C on chocolate agar (Fig. 5.4). Thayer Martin, New York City, Chacko Nair egg, Mueller Hinton media under 5-10% CO₂ (Candle jar) and produce five types of colonies (T₁T₅). T₁ and T₂ are usually seen in primary isolates, whereas T₃ and T₄ in subcultures, and they differ in certain properties.

Colonies are transparent disks of about pinhead, discrete, circular or with crenated margin.

Biochemically, they are oxidase positive, ferment glucose and not maltose.

4. Viability of Neisseria:

They die at 55°C in 5 minutes, are fragile and cannot resist an adverse conditions.

5. Antigenic Structure of Neisseria:

N. gonorrhoeae is antigenically heterogenous and its surface structures include the following:

(a) Pili;

(b) Protein I (Porin);

(c) Protein II;

(d) Protein III;

(e) Lipopolysaccharides;

(f) Other proteins.

(a) Pili:

These are hair like structures extending from the surface and measures about 7 mm in diameter. They are seen on the surface of fresh isolates. The piliated organisms produce altered appearance of colonies on culture media with sharply defined borders.

Pili help the attachment of organisms to the host cells and can recognise specific receptors on the surface of host cells. Though pilin proteins of almost all strains are antigenically different, a single strain can produce several antigenically distinct pilins.

(b) Protein I (Por):

Extends through the cell membrane and forms pores on the surface. Each strain of gonococcus possesses only one type of protein I; 18 serovars of Type I A and 28 servoars of type I B have been demonstrated by serotyping of protein I. Through the pores, some nutrients enter the cell. Molecular weight of por protein is 34, 00 to 37,000 Daltons.

(c) Protein II (Opa):

A portion of protein II is in the outer membrane and the rest is exposed on the surface of gonococci, which is responsible for their adhesion, within colonies and attachment to host cells. Opaque colonies formation by gonococci is due to Type II protein, molecular weight of Opa is 24,000 to 32,000 Daltons.

Not more than 3 Opa are expressed by one strain of N. gonorrhoeae, though every strain has about 10 genes for the expression.

(d) Protein III:

It is associated with protein I in cell surface in the formation of pores.

(e) Lipopolysaccharide (LPS) of N. gonorrhoeae:

Differs from that of Gram-negative bacilli in chemical structure as it does not possess long O-antigenic side chains. It is mainly responsible for endotoxic effects in gonorrhoeae.

(f) Other proteins:

They are poorly defined proteins. Gonococci produce Ig AI proteases which split and inactivate Ig AI. Lip (1-18) and Fbp (iron binding protein) are two other proteins. Their role in the pathogenesis is not yet established.

(g) Capsule:

Capsule is loosely associated with cell surface of fresh isolates on in vitro cultivated isolates, can be stripped off and can be synthesised from the environmental and nutritional factors. Gonococcal capsule is a polyphosphate and can prevent the phagocytosis. The role of capsule in infection needs to be studied further. N. acetyl neuramine acid, a constituent of eukaryotes, is only found in meningococcal capsule.

6. Pathogenicity and Clinical Features of Neisseria:

Their toxicity is due to endotoxin. In male, these organisms infect the mucosa of urethra with the help of pili and produce suppurative inflammation with purulent discharge (morning drop of secretion). At the early stage, these organisms are plenty in the discharge and later diminish due to association with secondary infection.

The infection spreads to the prostate, seminal vesicle and epididymis. The periurethral tissue is also infected—causing a periurethral abscess and structure.

In adult female, the urethra and cervix uteri are infected, not the vagina—as the vaginal mucosa of married women is stratified and acidic vaginal secretion—hence gonococci cannot get attached to the vaginal mucosa by their pili. Endometritis, salpingitis, peritonitis may occur.

In female infants and children, they may produce vulvovaginitis, but in newborn infants, ophthalmia neonatorum may ensure. Arthritis, tenosynovitis, ulcerative endocarditis, purulent conjunctivitis are the complications due to blood invasion.

7. Laboratory Diagnosis of Neisseria: Specimens:

In male, the meatus should be cleansed with sterile gauze soaked with sterile normal saline and the specimens are taken with the help of sterile wire loop or directly on slides.

In female, from the urethra or the cervix uteri with the wire loop or swabs are transported in Stuart’s transport medium.

Smears are stained with (a) Methylene blue, and (b) Gram’s stain; the presence of Gram-negative intracellular diplococci is suggestive of gonorrhoea.

In chronic infection, they are scanty; in male the “morning drop” of secretion should be examined.

8. Culture:

The diagnosis should be confirmed by the cultivation selective media and identification by oxidase and other biochemical tests.

A conglutination test is currently available which uses monoclonal antibody reactive with protein I (Porin) of N. gonorrhoeae. This test is sensitive (99.7%) and specific (100%) to identify this organism.

ELISA is sensitive and specific to detect gonococcal antigen in the urethral discharge. A biotinylated DNA probe can identify it in 10 minutes.

A liquid probe system with chemiluminescent detection system for direct detection of gonococci in the general specimens is equally sensitive as that of ELISA system.

Production of enzyme beta lactamase (Penicillinase) should also be ascertained for an effective therapy.

9. Treatment of Neisseria:

For penicillin resistant gonococci, spectinomycin, tetracycline, doxycycline and ceftriaxone are used. Resistance to spectinomycin and tetracycline has been reported.

10. Prevention and Control of Neisseria:

Gonorrhoea can be controlled by identification of cases, tracing of contacts, educating about spread of this disease through sexual contact and other general measures which will improve the health condition.

11. Non-Specific Urethritis:

Now the non-specific infection of urethra is considered as the most common sexually transmitted disease. It constitutes about 50% of all cases of urethritis and is predominant in males; but is symptomless in females.

The infection is caused by:

1. Bacteria – Chlamydia trachomatis (TRIC) is the most important causal agent. Urea-plasma urealyticum, Mycoplasma hominis, Gardner Ella vaginalis and Acinetobacter are also included.

2. Virus – Herpes and Cytomegalovirus

3. Fungus – Candida albicans

4. Protozoa – Trichomonas vaginalis.