Meningococci: Morphology, Feature and Prevention | Human Disease

In this article we will discuss about Meningococci (Neisseria Meningtidis) [which is a Human Disease] :- 1. Morphology and Staining of Meningococci 2. Antigenic Structure of Meningococci 3. Pathogenicity and Clinical Features 4. Laboratory Diagnosis 5. Prevention and Control 6. Cultural Character 7. Branhamella 8. Biochemical Reaction.

Contents:

1. Morphology and Staining of Meningococci
2. Antigenic Structure of Meningococci
3. Pathogenicity and Clinical Features of Meningococci
4. Laboratory Diagnosis of Meningococci
5. Prevention and Control of Meningococci
6. Cultural Character of Meningococci
7. Branhamella
8. Biochemical Reaction of Meningococci

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1. Morphology and Staining of Meningococci:

Under microscope, meningococci resemble gonococci morphologically, but biochemically they differ by their maltose fermentation reaction only (Fig. 27.1).

2. Antigenic Structure of Meningococci:

On the basis of capsular polysaccharide, 13 sero groups of meningococci have been identified. The most important serogroups associated with human disease are A, B, C, Y and W-135.

3. Pathogenicity and Clinical Features of Meningococci:

They may spread through the cribriform plate to the subarachnoid space by the olfactory nerve or they may attach to the sub mucosa of nasopharynx with the aid of pili, then reach the blood stream-bacteriaemia. Fulminant meningococcaemia is more severe with high fever and haemorrhagic rash; there may be disseminated intravascular coagulation and circulatory collapse.

Pyogenic meningitis in all ages including children and young adults are mainly caused by N. meningitidis. Other bacteria responsible for pyogenic meningitis are Haemophilus influenzae, Pneumococcus, Listeria monocytogenes; Leptospira interrogans can rarely causes this infection.

Serogroups A, B and C of N. meningitidis are common cause of meningococcal meningitis but in carriers other serogroups are often identified. Serogroups A causes epidemic meningitis in most countries.

Since human nasopharynx harbours N. meningitidis, the infection is mostly via droplet spray of infected respiratory secretions from the patients on carriers. In normal population, the incidence of carrier rate is about 10-20%, in household contacts of sporadic cases and during epidemics, it may rise to 40%.

The incubation period is about 3 days. The organisms may spread from nasopharynx to the meninges via blood stream; it may also spread along the perineural sheath of olfactory nerve. There is acute fever with petechial rash in skin and mucosa. Probably the pathogenicity is due to bacterial endotoxin during fulminating meningococcal septicaemia the adrenal insufficiency may occur.

Meningococcal meningitis is very common in children and infants. Asymptomatic carriage of avirulent strain may most probably produce bacterial antibodies to invasive strain. Meningitis usually begins suddenly with intense headache, vomiting, stiff neck and progresses to coma within few hours. smear and culture.

4. Laboratory Diagnosis of Meningococci:

Blood for culture; punctured material from petechiae and CSF for smear and culture.

Smear:

Gram stained smear from all specimens will show polymorphonuclear leucocytes with meningococci.

Culture:

Specimens are plated on Mueller Hinton, Chocolate or Thayer Martin medium and the growth is identified by oxidase test and fermentation reaction. Gonococci and meningococci form convex, glistening, elevated, mucoid colonies, 1-5 mm in diameter. Colonies are transparent or opaque, non-pigmented and haemolytic. Identification of serogroup can be done in a smear by using fluorescein isothiocynate containing antisera.

The Limulus test for endotoxin is useful for detection of meningitis caused by meningococci— if the organisms are present at more than 103³/cm³.

ELISA:

This test is not useful for the rapid diagnosis of meningitis. The availability of rapid immunodiagnostic tests (co-agglutination, CIEP and latex agglutination test) has made the diagnosis easier and sensitive. Latex agglutination test is now widely available and produces result within minutes of the testing of supernatant of CSF.

Treatment:

Penicillin is the drug of choice—Cefotaxime or Ceftriaxone. Chloramphenicol can be used in persons allergic to penicillin.

5. Prevention and Control of Meningococci:

Immuno-prophylaxis:

This can be done by meningococcal vaccines prepared from surface polysaccharides of a number of serogroups A, C, W 135 and Y.

The eradication of the bacteria from nasopharynx of close contacts of patients can be conducted by Chemoprophylaxis (Rifampicin, ciprofloxacin, minocycline).

Avoidance of over-crowding in living and working environment is an important control measure.

Neonatal Meningitis:

Coliform bacilli (Escherchia coli, Klebsiella, Proteus) are most common aetiological agents of neonatal meningitis; Streptococcus pyogenes may sometimes cause this infection. During delivery, the neonates may acquire the infection through infected mother’s vagina. Premature babies may also get infected.

(i) Gentamicin and penicillin

(ii) Chloramphenicol

(iii) Cefotaxime are administrated.

Other Neisseriae:

Neisseria lactaemia, N. sicca, N. subflava, N. cinera, N. mucosa, N. flavescens are the normal flora of respiratory tract and are important as they grow on selective media (Muller Hinton, Thayer Martin etc.).

6. Cultural Character of Meningococci:

Neisseria flava, N. perflava, N, sicca and N subflava are commensals and can be differentiated from the pathogenic Neisseriae by following method:

(a) Their primary isolation does not require CO₂

(b) They produce pigmented (yellow to greenish) colonies and most of them ferment a variety of carbohydrates.

7. Branhamella:

In 1970, a new genus Branhamella has been proposed on the basis of fatty acid content and it is now called as B. catarrhalis. Earlier, it was classified as a species of Neisseria which shared many characters with commensal Neisseria and it was named N. catarrhalis. It is normal flora of the upper respiratory and genital tract. Though this genus was later shifted genus Moraxella, it is still included in the genus Branhamella.

Morphology:

They are Gram-negative diplococci measuring 0.6-1 µm, oval, with adjacent sides flattened or rounded.

Culture:

On nutrient agar (ordinary medium) they form colonies with a smooth and glistening surface.

8. Biochemical Reaction of Meningococci:

This organism does not ferment carbohydrate but hydrolyses tributyrin—a test for its identification. It produces catalase and oxidase.

Pathogenicity:

B. catarrhalis is now recognised as a cause of lower respiratory tract infection, though it is normal flora of nasopharynx. It has been encountered in otitis media, meningitis, sinusitis, endocarditis. About 50% strains of B. catarrhalis produce beta-lactamase which are resistant to penicillin and ampicillin.

These commensal Gram-negative diplococci (Neisseria) occur on various mucous surfaces of the body and are found regularly in the mucous secretions of the throat, nose and mouth. Organisms of Genus Veillonella, Gram-negative cocci (.3 µ) occurring in masses as commensals in natural cavities of man—particularly the mouth and alimentary tract.

They do not prove pathogenic though sometimes isolated from cases of appendicitis (pyorrhoea) and pulmonary lesions and regarded as potentially pathogenic.