Morphology & Culture Characteristics of Corynebacterium diphtheriae
   

MORPHOLOGY AND CULTURE CHARACTERISTICS OF CORYNEBACTERIUM DIPHTHERIAE (DIPHTHERIA BACILLUS)

MORPHOLOGY OF CORYNEBACTERIUM DIPHTHERIAE

Shape – Corynebacterium diphtheriae is a Thin, slender rod-shaped (bacillus) bacterium with a tendency to clubbing at one or both the ends due to the presence of metachromatic granules which may present at one or both the ends.

Size – The size of Corynebacterium diphtheriae rods is about 3–6 µm × 0.6–0.8 µm.

Arrangement Of CellsCorynebacterium diphtheriae is arranged in the angular fashion resembling English letters ‘V’ or ‘L’ which is also called as “Chinese letter pattern” or “Cuneiform arrangement”. This unique arrangement of the C. diphtheriae is due to the incomplete separation of the daughter cells after cell division (by Binary fission).



MotilityC. diphtheriae is a Non-motile bacterium.

FlagellaCorynebacterium diphtheriae is a Non-flagellated bacterium

SporesC. diphtheriae is a Non-sporing Bacterium.

CapsuleCorynebacterium diphtheriae is a non-capsulated bacterium.

Gram Staining ReactionC. diphtheriae is a Gram +ve bacterium (but tend to decolorized easily).

Check out the Morphology & Cultural Characteristics of Streptococcus pneumoniae

CULTURE REQUIREMENTS OF CORYNEBACTERIUM DIPHTHERIAE

Special requirementsCorynebacterium diphtheriae requires enriched media for the growth and readily grows in a media containing Blood, Serum or Egg, commonly Loeffler’s serum slope & Tellurite Blood Agar medium is used for the cultivation of Corynebacterium diphtheriae in diagnostic laboratories. Also, on the ordinary medium like Nutrient Agar medium, the growth of C. diphtheria is scanty in amount.

 Optimum temperatureC. diphtheriae grows best at 37°C

⇒ Optimum pH – 7.4-7.6

⇒ Oxygen requirementsCorynebacterium diphtheriae 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.

morphology of corynebacterium diphtheriae - cultural charcateristics of corynebacterium diphtheriae - culture characteristics of corynebacterium diphtheriae

⇒ There are various culture media used for the cultivation of Corynebacterium diphtheriae in the laboratory and most commonly the Loeffler’s Serum Slope medium is used, the other media employed for the isolation of Corynebacterium diphtheriae are as follows –

  • Nutrient Agar medium (Growth is scanty)
  • Tellurite Blood Agar medium (selective medium)
  • Hiss’s Serum Water
  • Tinsdale medium is also a selective culture medium for the isolation of Corynebacterium diphtheriae
  • The liquid medium (Nutrient Broth medium, TSB medium, etc. can be used but the growth is scanty in amount)

⇒ The Tellurite Blood Agar medium which is the Selective medium for Corynebacterium diphtheriae can be prepared by incorporating Potassium Tellurite (0.04%) in the Blood Agar medium for the growth of Corynebacterium diphtheriae.



The Tinsdale Medium which is also a Selective medium for C. diphtheriae can be prepared in the laboratory by incorporating Bovine serum, Cysteine and Potassium tellurite in Sheep’s Blood Agar medium for the growth of Corynebacterium diphtheriae in the laboratory.

Check out the Morphology & Cultural Characteristics of Streptococcus pyogenes

CULTURE CHARACTERISTICS OF CORYNEBACTERIUM DIPHTHERIAE

Cultural CharacteristicsLoeffler’s Serum SlopeTinsdale Agar medium
Hemolysis-----Weak β- Hemolysis or No hemolysis (γ - Hemolysis)
ShapeCircularCircular with a brown  halo surrounding the colony
Size0.5-1 mm0.5-1 mm
ElevationLow ConvexLow Convex
SurfaceGlisteningGlistening
ColorWhite or CreamyBlack or Brown colonies
StructureOpaqueOpaque

The growth on tellurite blood agar medium varies considerably as per the biotype of Corynebacterium diphtheriae which is as follows:

Cultural Characteristics of C. diphtheriae on Tellurite Blood Agar mediumC. d. gravisC. d. intermediusC. d. mitis
HemolysisWeak β- Hemolysis or No hemolysis (γ - Hemolysis)No hemolysis (γ - Hemolysis)Weak β- Hemolysis or No hemolysis (γ - Hemolysis)
ShapeCircular & flatCircularCircular & flat
Size1-2 mm1 mmVariable size of colony
ElevationRaised center, crenated edges with radial striations (daisy head colony)Central elevationCentral elevation
SurfaceGlisteningGlisteningGlistening
ColorGreyGrey – BlackShiny Black
StructureOpaqueOpaqueOpaque

Similarly in liquid culture media like Hiss’s Serum water, and Nutrient broth or Glucose broth, the growth of the bacterium occurs as a turbidity with a surface pellicle formation which may vary as per the biotype of the C. diphtheriae (the C. diphtheriaegravis, intermedius and mitis described below) which is further analyzed for the morphology (under the microscope), gram reaction, biochemical tests, and Corynebacterium diphtheriae specific tests.

Cultural CharacteristicC. d. gravisC. d. intermediusC. d. mitis
Growth in Hiss’s Serum water or in Broth cultureSurface pellicleTurbidity (in 24 hr.), Clearing (48 hr.) with fine granular sedimentDiffused turbidity throughout the content

That’s All about the Morphology & Culture Characteristics of Corynebacterium diphtheriae



Further Reading:

Diphtheria Bacillus – Textbook of bacteriology

SAHIL BATRA

Hi, I'm the Founder and Developer of Paramedics World, a blog truly devoted to Paramedics. I am a Medical Lab Tech, a Web Developer and Bibliophiliac. My greatest hobby is to teach and motivate other peoples to do whatever they wanna do in life.

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