Since the last few posts focused around experiments with nutrient agar plates, I thought it would be beneficial to discuss how the observations are determined and recorded. When microorganisms are grown in agar, a colony appears where the original organism was. These organisms show visible differences in appearance in their colonies and growth. These physical appearances are often for a specific type of bacteria that is being grown on that colony, and can be used as a method of identification.When growing microorganisms on nutrient agar plates, it is important to observe the Size, Form, Margin, Elevation, Pigmentation, Texture, Appearance, and Optical Properties. The standards for identifying these physical appearances are as follows:
- Size
Pinpoint, small, moderate, large
- Form (shape of colony)
Circular (unbroken, peripheral edge), irregular (indented, peripheral edge), rhizoid (root-like, spreading growth), punctiform (tiny), filamentous, spindle
- Margin (appearance of outer edge of colony)
Entire (sharply defined, even, smooth), lobate (marked indentation, lobed), undulate (wavy indentation), serrate (tooth-like), curled, rhizoid (root-like), filamentous (threadlike, spreading edge)
- Elevation (the degree to which the colony growth is raised)
Flat (elevation not discernable), raised (slightly elevated), convex (dome-shaped), umbonate (raised, the elevated convex center region), pulvinate (very convex)
- Pigmentation (color of colony)
Nonpigmented (cream, tan, white) or Pigmented (purple, yellow, black)
- Texture
Smooth or rough
- Appearance
Shiny & glossy, dry & powdery, wrinkly
- Optical Properties
Opaque (no light transmitted),
translucent (partial light transmission), transparent
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