Neisseria Meningitides (Meningococcus)

Neisseria Meningitides (Meningococcus)

The genus Neisseria is included in the family Neisseriaceae (Figure 7.6). It contains two important pathogens Neisseria meningitidis and Neisseria gonorrhoeae, both the species are strict human pathogens. N. meningitides causes meningococcal meningitis (formerly known as cerebrospinal fever).

The word Meningitis is derived from Greek word ‘meninx’ means membrane and ‘itis’ means inflammation. It is an inflammation of meanings of brain or spinal cord. Bacterial meningitis is a much more severe disease than viral meningitis.

Morphology

They are Gram negative diplococci (0.6µm–0.8µm in size) arranged typically in pairs, with adjacent sides flattened.

They are non – motile, capsulated (Fresh isolates).

Cocci are generally intracellular when isolated from lesions (Figure 7.7).

Cultural Characteristic

They are strict aerobes, but growth is facilitated by 5–10% CO₂ and high humidity. The optimum temperature is 35°C–36°C and optimum pH is 7.4–7.6. They are fastidious pathogens, growth occurs on media enriched with blood or serum. They grow on the following media and show the characteristic colony morphology (Table 7.4).

Pathogenesis

N. meningitidis is the causative agent of meningococcal meningitis, also known as pyogenic or septic meningitis. Infection is most common in children and young adults. Meningococci are strict human pathogens. Human nasopharynx is the reservoir of N.meningitidis. The pathogenesis is dicussed in the flowchart 7.2

Source of infection – Airborne droplets

Route of entry – Nasopharynx

Site of infection – Meninges

 Incubation period – 3 days

Laboratory Diagnosis

Specimens: CSF, blood, nasopharyngeal scrapings from petechiae lesions are the specimens collected from pyogenic meningitis patients.

Direct Microscopy: CSF is centrifuged, and smear is prepared from the deposit for gram staining. Meningococci are Gram negative diplococci, present mainly inside polymorphs and many pus cells are also seen.

Culture: The centrifuged deposit of CSF is inoculated on chocolate agar. The plate is incubated at 36°C under 5–10% CO₂ for 18–24 hours. After incubation period, meningococcusis identified by gram staining, colony morphology and biochemical reactions. N. meningitides is catalase and oxidase positive (Figure 7.8).

Treatment and Prophylaxis

Penicillin – G is the drug of choice. In penicillin allergic cases, chloramphenicol is recommended.

• Monovalent and polyvalent vaccies (capsular polysaccharide) induce good immunity in older children and adults

•.Conjugate vaccines are used for children below the age of 2 years.