Heat Fixed Microscope Slide of Bacteria

How to Prepare a Microscope Slide of Bacteria
Heat Fixing a Bacterial Smear for Staining


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.

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 
Heat Fixed and Gram Stained Slide of Bacteria
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.

How To Prepare a Bacterial Smears

Heat Fixing the Bacterial Sample
Before staining, the sample must be heat fixed. This process accomplishes three things:
  • kills the bacteria
  • firmly attaches the smear to the microscope slide
  • allows the sample to more readily take up the stain
Slides heat fixing on tray attached to microincinerator
Slides heat fixing on tray attached to microincinerator.
​Page last updated 3/2016

How to Prepare a Bacterial Smear for Gram Staining
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.

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.
  • Gently mix the bacteria into the water drop.

Instructor's Corner
Staining Bacteria
Go to PAGE 2 >

Photographic guides to differential stains 
now available!

1. Gram
2. Acid-fast
3. Endopsore

How to Prepare a Bacterial Smear for Acid Fast Staining
How to Prepare a Bacterial Smear for Endospore Staining
Science Image Library Bacterial Stains
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Heat Fixed Microscope Slide of Bacteria
Bacterial smear after heat fixing and before staining. Positive bacterial control in circle on the left, negative control on right, and unknown bacteria in center circle. 
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Prokaryotic Cell, Mariana Ruiz