Colony Characteristics of Bacteria

The visual properties of a bacterial colony observed on a culture media are known as colony morphology. An essential ability for identifying bacteria in the microbiology lab is observing colony morphology. To examine the distinctive form, size, colour, surface texture, and isolation from other colonies, colonies must be kept well apart. Hemolysis is another crucial feature of a bacterial colony. The lysis of the blood cells that make up Blood Agar results in hemolysis.

Morphology of Bacterial Colony

Procedure

The bacterial specimen is placed in an incubator after being seeded onto an agar plate to promote microbial growth. Colonial morphology is evaluated at a specified time after the plate is inoculated since the appearance of microbial colonies varies as they proliferate. The plate is typically read 18 to 24 hours after inoculation, while slower-growing organisms like fungus may require a different time frame. After that, details such as the size, colour, form, consistency and opacity of the colony are noted.

Characteristics of Bacterial Colony

The appearance of the bacterial colony on the culture medium is usually the characteristic feature for the identification of the bacterial species. The following are the features of the bacterial colony that are typically observed:

• Surface Appearance – Can be smooth, rough/granular, dull, shiny or wrinkled.
• Size – A representative bacterial colony’s diameter can be measured in millimetres and can be categorised as large (>1 mm), medium (=1 mm), small (<1 mm) and pinpoint (<0.5 mm).
• Shape – Circular, irregular, rhizoid or filamentous.
• Texture or consistency – Brittle/friable (dry, breaks apart), firm, butyrous (buttery) and mucoid (sticky, mucus-like).
• Elevation – Colony may be raised, flat, convex, umbonate, pulvinate and crateriform.
• Edge – Entire, lobate, crenated, undulate or ciliate.
• Colour – Pigments are produced by certain bacterial species. Prodigiosin is an orange-red pigment that is produced by Serratia marcescens. The pigments pyoverdin and pyocyanin, which are produced by Pseudomonas aeruginosa, give the colonies a greenish sheen.
• Opacity – Transparent, translucent or opaque.
• Haemolysis – Haemolysin produced by some bacteria leads to haemolysis around the colony. Based on that, the bacterial colony can be:

1. Alpha – Partial destruction of blood cells.
2. Beta – Complete destruction of blood cells.
3. Gamma – No destruction of blood cells.

Also Check: MCQs on Morphology of Bacteria

Sometimes, the odour (smell) of the culture and the motility of the bacterial species might also be considered. For example, the odour of the Pseudomonas aeruginosa colony is similar to grapes. Likewise, organisms with swarming motility have concentric waves of proliferation that radiate from the point of inoculation.

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Do Check:

• Shapes of Bacteria
• Classification of Microorganisms