Disease caused by Neisseria meningitidis

 Neisseria meningitidis.

Introduction

  • 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.
Neisseria meningitidis
Neisseria meningitidis

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.

4. Resistance

  • 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.

5. Pathogenecity

  • 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.

6. Epidemiology

  • 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.

8. Treatment

  • 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.

 

 

 

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