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This article throws light upon the four main growth characteristics of a pure culture of bacteria. The growth characteristics are: 1. Colonies on Agar Media 2. Growth on Agar Slants 3. Growth in Gelatin or Agar Stabs 4. Growth in Broth.
Pure Culture: Characteristic # 1. Colonies on Agar Media:
The bacterial culture is mixed with gelatin or agar melted previously by heat and partially cooled. The mixture is then allowed to cool, set in petridish and incubated for development of colonies.
The following characteristics of the colonies are usually observed:
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Form:
Normally colonies are circular but other forms like rhizoid, irregular etc. can also be observed.
Size:
Colonies present a wide variation in their size. They may be very small and restricted to large spreading occupying the entire surface of the petridish.
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Elevation:
The colonies may be flat and thin or thick with convex, pulvinate or other types of surface.
Contour:
The surface of the colonies may be smooth or wrinkled. They may also exhibit point-like elevation.
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Surface:
Usually the surface of the colonies is glistening. However, colonies with dull surface may also be encountered.
Texture:
Most colonies are soft and slimy but some are dry and brittle, while few are viscid.
Colour:
Generally bacterial colonies are greyish white. Various shades of yellow and pure white are commonly observed.
Other colonies with red, orange, blue, green etc. colours also occur.
Pure Culture: Characteristic # 2. Growth on Agar Slants:
Agar slant cultures are prepared by streaking the slanting surface of the medium in a tube with a stroke of an inoculating needle.
Pure Culture: Characteristic # 3. Growth in Gelatin or Agar Stabs:
The inoculation needle having the inoculum is pierced in a straight line from top to bottom of the tube and withdrawn along the same path.
Pure Culture: Characteristic # 4. Growth in Broth:
The tubes containing nutrient broth are inoculated with the help of the transferring needle or loop.
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