Colony Morphology

Understanding Colony Morphology in Bacteria

What is Colony Morphology?

• Colony morphology refers to the physical appearance of bacterial colonies on a growth medium, such as TSA plates. Different appearances can indicate different species of bacteria, although identical-looking colonies may still belong to different species.

Characteristics of Colony Morphology

• There are six key characteristics used to describe colony morphology: size, color, texture, shape, elevation, and margin. A magnifying glass included in the supply box helps observe these features more effectively.

Size and Color

• The size of bacterial colonies can be subjective; what one person considers medium-sized might be viewed as large by another. Most environmental colonies tend to be white or off-white but can also appear in various colors like yellow, orange, brown, blue, green, pink, or black.

Texture and Shape

• Texture is determined by moisture retention within the colony: dry colonies appear flat while moist ones look shiny. Shapes include punctiform (tiny), circular (round), filamentous (stringy), irregular forms, rhizoid (root-like structures), and spindle-shaped colonies.

Elevation and Margin Descriptions

Elevation Types

• Elevation describes how much a colony protrudes above the surface of the medium:

• Flat: does not stick out

• Raised: slightly elevated

• Convex: rounded top

• Pulvinate: very pronounced rounded top

• Umbonate: convex with a prominent center

• Crateriform: convex with a central dip resembling a volcano

Margin Characteristics

• The margin refers to the outer edge of the colony:

• Entire: smooth margin

• Undulate: wavy margin

• Lobate: pronounced waves

• Filamentous shapes do not have a defined margin description and are simply termed filamentous.