How to Identify Bacteria Growing in Agar
Colonies of bacteria occur when one single microbe multiplies and produces identical offspring. To identify bacteria in agar solution in a petri dish, look at the characteristics of the colony, or colony morphology. Bacteria tend to have predictable characteristics.
Instructions
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Sort bacteria according to size. Decide if it is small, medium or large. For example, the bacteria that causes strep throat is about three micrometers big.
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Sort the colonies according to shape. They can be circular, irregular or rhizoid. For example, Staphylococcus, which can cause food poisoning, has a distinctive round shape.
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Sort the colonies according to edge. The edges can be smooth, filamentous or undulating. For example, M. luteus, which grows in the mouth, has a smooth edge.
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Sort the colonies based on pigmentation and color. Bacteria are usually red, yellow or white. The bacteria that live in the Red Sea have a characteristic red color.
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Sort the colonies according to elevation. Possible elevations are flat, raised, convex or crateriform. One example of this is the Staphylococcus bacteria, which is convex.
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Sort the colonies according to surface. Possible surface appearances are wrinkled, rough, waxy and glistening.An example of a waxy bacteria is Mycobacterium smegmatis, which is often used in laboratories.
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Sort the colonies according to opacity. This means the amount of transparency in the bacteria. One transparent bacteria is the virus that causes strep throat.
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Tips & Warnings
The type of plate is also important to identifying the bacteria. According to the biology department at Davidson, some bacteria break down red blood cells, and some don't. This concept is useful when identifying Streptococcus pyogenes. This bacterium, which causes strep throat, breaks down red blood cells on the agar completely. The rest of the microbes in the throat would only partially break down the agar.
References
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