First, use a wax pencil to draw a circle on the microscope slide to separate each type of bacteria that is going to be sampled. If a simple stain of only one type of bacteria, or single mixed sample of bacteria is being prepared, no separation is required.
Preparing a Bacterial Smear
In order to be able to clearly see individual bacteria, a sample of a bacterial colony must be mixed into water or physiological saline. This helps to evenly spread out the bacterial sample.
Article Summary: In order to view individual bacteria through a light microscope, a bacterial smear must be attached to a slide and then stained. Here is the procedure.
How to Prepare & Heat Fix a Bacterial Smear for Staining
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Bacterial smear that has been heat fixed and stained.
In order to heat fix a bacterial smear, it is necessary to first let the bacterial sample air dry. Then either place the slide in the slide holder of a microincinerator, or pass the dried slide through the flame of a Bunsen burner 3 or 4 times, smear side facing up. Once the slide is heat fixed, it can then be stained.
MICROBIOLOGY VIDEO COLLECTION: How To Prepare a Bacterial Smears
Heat Fixing the Bacterial Sample
Before staining, the sample must be heat fixed. This process accomplishes three things. It functions to:
kill the bacteria
firmly affix the smear to the microscope slide
allow the sample to more readily take up the stain
Slides heat fixing on tray attached to microincinerator.
Page last updated 3/2015
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SPO VIDEO: How to Prepare a Bacterial Smear for Gram Staining
Placing the Bacterial Sample on the Slide
Place a drop of water into the wax circle that has been created on the slide.
Using a sterilized and cooled inoculation loop, obtain a very small sample of a bacterial colony.