Draughtsman Appearance: Colonies Structure & Morphology

Streptococcus pneumoniae (pneumococci), a human microbial pathogen, responsible for pneumatic infection in the 19th century. And it can be diagnosed by Draughtsman Appearance of their colonies.

Draughtsman appearance is an indicative culture-based test for Pneumococcus (Streptococcus pneumoniae). They are usually seen in 24 – 48 hrs of prolonged incubation in blood agar as young alpha-hemolytic colonies with flattened-depressed centers. This appearance is also called Carrom Coin Colonies.

But, there is more to know here about the Draughtsman colonies and their appearance.

What are Draughtsman Colonies?

Draughtsman Colonies— also called carrom coin colonies—  are the result of prolonged incubation of inoculating samples onto blood agar. The incubation time majorly ranges from 24 – 48 hours. 

In 24 to 48 hours, Young alpha-hemolytic colonies appear to flatten with a depressed center like concentric rings and central umbonation. 

These flattened concentric rings are because of partial autolysis. And these colonies are called be Draughtsman Colonies of Pneumococci. 

Other Names of Draughtsman Colonies?

Other names are:

• Draughtsman Appearance
• Carrom Coin Colonies Appearance
• Streptococcus pneumoniae colonies

More About Streptococcus Pneumoniae

Streptococcus Pneumoccoi — medically known as the pneumococcus — is gram-positive bacteria, normally present in the human upper respiratory tract.

They have lancet-shaped cocci and usually occur in pairs or in short chains with an individual diameter between 0.5 and 1.25 micrometers in diameter.

They are fastidious bacteria with the best growth seen in temperature in between 35 to 37°C with about 5% of carbon dioxide (CO₂) (or in a candle-jar).

Infections such as pneumonia, paranasal sinusitis, meningitis, and otitis media are caused by these bacteria. 

How to Test Pneumococcus Using Draughtsman Appearance?

Material Required:

• Blood Agar as Fastidious bacterial growth medium
• Inoculate sample sputum/CSF)
• Thermal Incubator

Procedure:

1. Take 10 microliters from appropriately diluted samples with the help of a micro-pipettor.
2. Place the sample on the surface of the agar medium.
3. Incubate the agar medium into the incubator for 24 to 48 hours at 37°C with 5-10% CO₂.

Structural and Morphology of Draughtsman Colonies

In the incubation period, colonies on the blood agar plate appear to be:

• Small (diameter of 0.5mm)
• Round
• Translucent
• Green, α-hemolytic, zone surrounds S. pneumoniae colonies

In 24 to 48 hours of incubation, due to partial hemolytic, these tentatively colonies have a:

• Flattened or concentric ring, with
• Depressed center or central umbonation

Draughtsman Colonies in S. Pneumococci Vs S. Viridans

This culture-based Draughtsman test can be used as a characteristic test for differentiating Streptococcus Viridans with Streptococcus Pneumococci.

Both Streptococcus Viridans and S. Pneumococci bacterias produce alpha-hemolytic colonies. But, only S. Pneumococci produce a draughtsman colony.

Other Test For Pneumococcus

A. Gram Staining and Microscopic Observations

Procedure: 

1. Apply, crystal violet stain to a heat-fixed smear of S. Pneumococci.
2. Addition of iodine to the cultured sample.
3. Rapid decolorization with ethanol.
4. Counterstaining with safranin.

Microscopic Observation: Gram-positive lanceolate shaped diplococci.

B. Biochemical Optochin Test

Procedure:

1. Inoculation is done with a suspected alpha-hemolytic sample.
2. Apply optochin discs (6 mm disc with 5µg) on the blood agar isolate.
3. Incubate the agar medium into the incubator for 24 to 48 hours at 37°C with 5-10% CO₂.

Observation: Zone size greater than 14mm is a characteristic of S. pneumoniae.

C.  Bile Solubility Test

In the bile solubility test, those alpha-hemolytic colonies on optochin discs with zone sizes of 9 to 13 mm are viable for this test.

Procedure:

1. With the turbidity of 0.5 McFarland, prepare 1 ml of saline suspension from the optochin disc.
2. Divide half (each 0.5 ml) into two separate tubes.
3. 0.5 ml of 2% Sodium deoxycholate is added in one tube and prepared 0.5 ml of saline in the second tube.
4. After gently shaking, incubate both the tubes for 2 hours at  37°C

Observation: If turbidity persists, a clear indication of the absence of S. Pneumococci. However, loss in turbidity—due to disruption of cells— an indication of Pneumococcus.

Test Your Knowledge

1. Draughtsman’s appearance are seen in

1. Pneumococcus
2. Streptococcus
3. Staphylococcus
4. None of the above

2. What are the other names of Draughtsman appearance?

1. Carrom Coin Appearance
2. Paper boat appearance
3. Carrom Disk Appearance
4. Both (1) and (3)

3. Draughtsman appearance of pneumococci is due to

1. Tentative hydrolysis of pneumococci
2. Partial autolysis of pneumococci
3. Partial hydrolysis of pneumococci 
4. Partial hemolytic of pneumococci

4. What of the following is correct for the structural morphology of Draughtsman colonies?

1. Flattened with central umbonation
2. Concentric ring with depressed center
3. Flattened with an elevated center
4. Both (1) and (2)

5. Which of the following is the best incubation condition for Draughtsman appearance test?

1. 32°C for 24 to 48 hours
2. 34°C for 24 to 48 hours
3. 37°C for 24 to 48 hours
4. Both (2) and (3)

 Reference:

• https://pubmed.ncbi.nlm.nih.gov/3584479/[Link]
• How to identify Streptococcus pneumoniae? by Microbeonline.com
• Microbiology Diagnosis: Streptococcus pneumoniae [link]
• Streptococcus pneumoniae [link]

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