MORPHOLOGY OF NEISSERIA MENINGITIDIS (MENINGOCOCCUS)
Shape – Neisseria meningitidis is an oval or spherical (coccus) shape bacterium with the adjacent side flattened.
Size – The size of Neisseria meningitidis is about 0.6 µm – 0.8 µm (micrometer).
Arrangement Of Cells – Neisseria meningitidis is arranged in pairs (diplococci), with the adjacent side flattened and they are usually present intracellularly when direct microscopic examination of the specimen from the lesions is carried out.
Motility – Neisseria meningitidis is a Non-motile bacterium.
Flagella – Neisseria meningitidis is a Non-flagellated bacterium
Spores – Neisseria meningitidis is a Non-sporing Bacterium
Capsule – N. meningitidis is a capsulated bacterium and is present in such a way that a capsule encloses each pair of cocci. The capsule can easily be demonstrated using India ink preparation, appear as a clear halo in a dark background. Moreover, the presence of capsule depends on the origin of the specimen as the specimen taken from the carrier may or may not contains encapsulated N. meningitidis whereas the sample isolated from CSF (cerebrospinal fluid) or from blood usually contains encapsulated N. meningitidis.
Gram Staining Reaction – Neisseria meningitidis is a Gram –ve (Negative) bacterium.
CULTURE REQUIREMENTS OF NEISSERIA MENINGITIDIS (MENINGOCOCCUS)
⇒ Special requirements – Meningococci or Neisseria meningitidis have complex nutritional requirements and readily grow in a media containing Blood or Serum, commonly Blood Agar medium, Chocolate Agar medium & Mueller Hinton Agar medium is used for the cultivation of Neisseria meningitidis in Laboratory.
⇒ Optimum temperature – Neisseria meningitidis grows best at 35 –36°C
⇒ Optimum pH – 7.4-7.6
⇒ Oxygen requirements – N. meningitidis (Meningococcus) is an obligate Aerobic bacterium i.e. can only grow in the presence of oxygen in optimum amount and cannot grow in the low oxygen environment.
⇒ It requires a moist environment with a 5 – 10% CO2 for the growth in the laboratory.
⇒ There are various culture media used for the cultivation of N. meningitidis (Meningococcus) in the laboratory and most commonly the Blood Agar and MHA medium is used, the other media are as follows –
- Sheep Blood Agar medium
- Columbia Horse Blood Agar medium
- Chocolate agar medium
- Thayer Martin medium with Antibiotics Vancomycin, Colistin and Nystatin (selective medium)
- Modified Thayer Martin medium with Antibiotics Vancomycin, Colistin, Nystatin & Trimethoprim (selective medium)
- Martin – Lewis medium (selective medium)
- New York city medium (selective medium)
- The liquid medium (Glucose Broth medium, TSB medium, Peptone water etc.)
⇒ The Thayer Martin medium which is Selective medium for Neisseria meningitidis can be prepared by incorporating Antibiotics and Nutrients in Thayer Martin Agar base or in GC Agar base medium for the growth of Neisseria meningitidis (Meningococcus).
⇒ Similarly, the New York City medium which is also a selective medium for Neisseria meningitidis can be prepared by incorporating Antibiotics and Supplementary nutrients in the NYC Agar Base medium for the Growth of Neisseria meningitidis (Meningococcus)
CULTURE CHARACTERISTICS OF NEISSERIA MENINGITIDIS (MENINGOCOCCUS)
Culture Characters Blood Agar Medium (BAM) Thayer Martin Medium New York City Medium Chocolate Agar Medium (CAM)
Shape Circular or Round Circular or Round Circular or Round Circular or Round
Size 1-1.5 mm 2-3 mm 1 -2 mm 1 -2 mm
Elevation Convex Convex Convex Convex
Surface Smooth, Moist & Glistening Smooth, Moist & Glistening Smooth, Moist & Glistening Smooth & Moist
Color Grey Colorless to Grey Colorless to Grey Colorless to Grey
Structure Opaque Transparent or Opaque Transparent or Opaque Opaque
Hemolysis γ – Hemolysis (No hemolysis) γ – Hemolysis (No hemolysis) γ – Hemolysis (No hemolysis) γ – Hemolysis (No hemolysis)
In liquid culture media like peptone water and TS broth or Glucose broth, the growth of the bacterium occurs as a Granular turbidity in the broth medium which is further analyzed for the morphology (under the microscope), gram reaction, biochemical tests, and Neisseria meningitidis specific tests.