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AAT Bioquest

What is the procedure of direct stain using a basic dye?

Posted March 9, 2023


Answer

Before direct staining, one must first make bacterial smears. First, a small drop of saline must be added to the slide. Then, an inoculation loop is used to pick up a small quantity of bacteria. The bacteria is then mixed with the saline and spread over a wide area of the slide. The smear should then be air dried, and heat fixed with a Bunsen burner. After creating smears, place the heat-fixed slide onto a slide rack over a sink. One must cover each smear with one or more drops of the stain reagent and allow the stain to sit for the proper amount of time. The next step is to remove the slide from the stain rack, and hold it at an angle facing the bottom of the sink to rinse it with tap water. In the third step, excess water is removed using a paper towel and the smear surface must be air-dried. The dried smears are then ready to be observed under a microscope. Once under the microscope, the 10X objective lens should be used to focus the lens on the microscope. Once it is focused, the 40X objective lens should be used to focus the specimen again. Then, oil immersion should be applied to the slide to view the specimen at the 100X objective. At this point, one can draw the microbial cells seen in the microscopic field. 

Additional resources

Staining and Interpretation of Smears

Cell Sample Preparation

Immunohistochemistry (IHC)

DAPI [4,6-Diamidino-2-phenylindole, dihydrochloride] *10 mM solution in water*