Overview
This lecture covers the concept of colony morphology, explaining how to observe and record the characteristics of microbial colonies for identification purposes.
Definition and Importance of Colony Morphology
- Colony morphology refers to the visible characteristics of a microbial colony on an agar plate.
- A colony forms from the multiplication of a single mother cell under favorable conditions.
- All cells in a colony are genetically identical and share the same traits.
- Observing colony morphology helps differentiate between colonies and identify microorganisms.
Key Colony Characteristics
- Size: Measured in millimeters or described as pinpoint (punctiform), small, medium, or large; larger bacterial colonies (>5mm) suggest motility.
- Shape (Form): Four main types—circular, irregular, filamentous, and rhizoid.
- Margin: Edge of the colony; can be entire (smooth), undulate (wavy), lobate (long lobes), curled, or filamentous.
- Elevation: Side-view appearance—flat, raised, umbonate, crateriform, convex, pulvinate, or a raised margin.
- Consistency (Texture): Described as dry, moist, viscid (sticky), brittle/friable, mucoid (slimy), or butyrous (butter-like).
- Surface Appearance: Colonies may appear shiny, smooth, dull, veined, rough, wrinkled, or glistening.
- Color (Pigment Production): Some bacteria produce characteristic pigments (e.g., green in Pseudomonas, red-orange in Serratia, yellow in Staphylococcus aureus).
- Opacity: Colonies can be transparent, translucent, opaque, or iridescent (color-changing in reflected light).
- Gram Staining & Motility: Identification includes Gram reaction (Gram-positive/negative rods/cocci) and motility; fungi use different staining.
Example: Bacillus Colony Characteristics
- Size: 8mm
- Shape: Circular
- Margin: Entire
- Elevation: Raised
- Consistency: Butyrous (cream-like)
- Opacity: Opaque
- Colour: White
- Gram Staining: Gram-positive rods
- Motility: Non-motile
Key Terms & Definitions
- Colony — a visible mass of microorganisms originating from a single mother cell.
- Margin — the edge or border of a colony.
- Elevation — the side-view profile of a colony.
- Consistency — the texture of the colony, such as dry or mucoid.
- Opacity — the degree to which light passes through a colony.
Action Items / Next Steps
- Practice identifying and recording colony morphology from agar plates.
- Prepare a table of colony characteristics for cultures observed in lab.