MORPHOLOGY OF STREPTOCOCCUS PNEUMONIAE (PNEUMOCOCCUS)
Shape – Streptococcus pneumoniae is an elongated round shape (coccus) bacterium with one end broad or rounded and the other end is pointed (flame shape or lanceolate appearance).
Size – The size of Streptococcus pneumoniae is about 1 mm (micrometer).
Arrangement Of Cells – Streptococcus pneumoniae is arranged in pairs (diplococci), with a broad end in apposition and the long axis of the coccus parallel to the line joining the two cocci.
Motility – Streptococcus pneumoniae is a Non-motile bacterium.
Flagella – Streptococcus pneumoniae is a Non-flagellated bacterium
Spores – Streptococcus pneumoniae is a Non-sporing Bacterium
Capsule – S. pneumoniae 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.
Gram Staining Reaction – S. pneumoniae is a Gram +ve bacterium.
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CULTURE REQUIREMENTS OF STREPTOCOCCUS PNEUMONIAE (PNEUMOCOCCUS)
⇒ Special requirements – Pneumococci or Streptococcus pneumoniae have complex nutritional requirements and readily grows in a media containing Blood, Serum or Sugars, commonly Blood Agar medium is used for the cultivation of Streptococcus pneumoniae.
⇒ Optimum temperature – Streptococcus pneumoniae grows best at 37°C
⇒ Optimum pH – 7.4-7.6
⇒ Oxygen requirements – S. pneumoniae (Pneumococcus) is an Aerobic and Facultative anaerobic bacterium i.e. can tolerate high levels of oxygen as well as readily grows in an environment with the low level of oxygen too.
⇒ There are various culture media used for the cultivation of S. pneumoniae (Pneumococcus) in the laboratory and most commonly the Blood Agar and PNF medium is used, the media are as follows –
- Nutrient Agar medium
- Sheep Blood Agar medium
- Columbia Horse Blood Agar medium
- Crystal Violet-Nalidixic acid-Gentamycin Agar medium (selective medium)
- The liquid medium (Glucose Broth medium, TSB medium, Peptone water etc.)
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⇒ The Crystal Violet-Nalidixic acid-Gentamycin Agar (CVNG) medium which is the Selective medium for Streptococcus pneumoniae can be prepared by incorporating Crystal violet, Nalidixic acid and Gentamycin in the Columbia Agar base or Blood agar base medium for the growth of Streptococcus pneumoniae (Pneumococcus).
CULTURE CHARACTERISTICS OF STREPTOCOCCUS PNEUMONIAE (PNEUMOCOCCUS)
| Cultural Characters | NAM (Nutrient Agar Medium) | Blood Agar Medium (BAM) | Crystal Violet- Nalidixic acid – Gentamycin (CVNG) Agar medium |
|---|---|---|---|
| Shape | Circular | Circular | Circular |
| Size | 0.5-1 mm | 0.5-1 mm | 0.5-1 mm |
| Elevation | Dome- Shaped or flattened colonies | Dome- Shaped in fresh cultures | Dome- Shaped |
| Surface | Glistening or Mucoid (due to Capsule production) | Glistening or Mucoid (due to Capsule production) | Glistening or Mucoid (due to Capsule production) |
| Color | Clear, Whitish or Very light Yellow as per the strain | Clear, Whitish or Very light Yellow as per the strain | Clear, Whitish or Very light Yellow as per the strain |
| Structure | Transparent or Opaque | Transparent or Opaque | Transparent or Opaque |
| Hemolysis | ----- | α – Hemolysis (Transparent or Opaque colonies surrounded by an area of Green Discoloration) | ----- |
On prolong incubation of the culture, the colonies become flat with raised edges and central umbonation, concentric rings are seen on the surface when viewed from above and appear as the Draughtsman or Carrom coin-like.
Moreover, the structure of the colonies on the culture media varies from transparent to opaque as per the strain of the Streptococcus pneumoniae. Some strains especially that are the part of Nasopharynx are usually produce transparent colonies and those which causes Bacteremia or Septicemia produce opaque colonies.
In liquid culture media like peptone water and Nutrient broth or Glucose broth, the growth of the bacterium occurs as a uniform turbidity in the broth medium which is further analyzed for the morphology (under the microscope), gram reaction, biochemical tests, and Streptococcus pneumoniae specific tests.
That’s All about the Morphology & Culture Characteristics of Streptococcus pneumoniae
Further Reading :
S. pneumoniae in textbook of bacteriology
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