- It is a gram negative, non-motile cocci arranged in pairs called as diplococci.
- Neisseria are aerobic, non-sporulating, oxidase positive cocci.
- Neisseria meningitidis causes cerebrospinal fever that is Meningococcal meningitis.
1. Morphological characters
- They are gram negative,spherical shape cocci with flattened adjacent side.
- Its size ranges from 0.6-0.8 micrometer.
- Its size,shape and staining properties changes as the incubation period increases.
- Fresh culture cells are capsulated and as the culture becomes old its capsule disappears.
2. Cultural characters
- Meningococci requires enriched media for its growth.
- The growth media should be enriched with blood or serum.
- Selective media like blood agar, chocolate agar, Mueller-Hinton starch casein agar are commonly used.
- The optimum temperature required for its growth is 36°C and optimum pH is 7.5-7.6
- The colonies are small in size bluish grey coloured and convex in elevation.
3. Biochemical reaction:-
- Oxidase test is positive in case of Neisseria so it is used for identification.
- It shows catalase test positive and nitrate reduction test negative.
- It can ferment glucose and maltose by production of acid and no gas.
- It is unable to utilise sucrose and lactose.
- Neisseria meningococci are very are very sensitive organisms.
- It is sensitive to heat, disinfection,pH changes and some antibiotics like penicillin but now many resistant strains are developed.
- Meningococci infection spread from nasopharynx to perineural sheath of olfactory nerve and from perineural sheath to cribriform plate to the subarachnoid space.
- Meningococci can infect through blood stream,or may enter by conjunctive.
- After infection to central nervous system supparrative lesion on spinal cord are formed.
- The untreated patients may suffer from blindness,deafness and recurrent meningitis.
- Human nasopharynx is the only in habitat of Meningococci.
- Air born droplets or droplet nuclei is the mode of transmission .
- It is common infection in children of age between 3 months to 5 years.
7. Laboratory diagnosis
1. Examination of cerebrospinal fluid:- The cerebrospinal fluid is collected and divided into three parts.
a) Part I
- The first portion is centrifuged.
- The residue is used for gram staining and Meningococci inside the polymorphs are observed this observation is sufficient to start antibiotic treatment.
- Now the supernatant is collected and this supernatant has antigens and these antigens are detected by latex agglutination test.
b) Part II
- The second portion is plated on blood and chocolate agar and incubated at 36°C for 24 hours.
- After incubation the organism is identified by its morphological, cultural, and biochemical characters.
c) Part III
- The third portion is added in equal amount of glucose broth and incubated overnight after overnight incubation this culture is subcultured on chocolate agar.
- Previously sulphonamide drugs were used but the organism have developed resistance againts it.
- Penicillin G, Cephalosporin, Chloramphenicol drugs are used in initial treatment.
- Later the treatment of Rifampicin or Ciprofloxacin is given.