Once a bacterial sample is heat fixed to a microscope slide, there are many staining techniques that can be used to view the bacteria. A simple stain is the use of one dye to increase contrast between the specimen and background when viewed through a microscope.
Tutorial on Compound Light Microscope Parts & Operation
When doing a differential stain it is best to use known positive (+) and negative (-) bacterial controls in addition to the unknown bacteria that is being identified. Controls allow for comparison of the unknown to a known bacteria that tests positive for that stain and another that is a known negative.
The following are examples of bacterial controls that could be used in differential stains:
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