Gram staining is a procedure which is carried out to identify whether bacteria are Gram positive or Gram negative. This is usually the first procedure done in the process of diagnosing a bacterial infection. Gram positive bacteria have cell walls which allow the stain to absorb into the cell, so they will show up as a purple colour after the staining procedure.
The process is:
1. Prepare a slide of the sample you wish to analyse. This can be blood, sputum, tissue etc. In this case, we were using stored samples of the various bacteria so I could have a look at them.
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| Cultured plates |
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| Slides |
2. Once the slides have been prepared and dried, the gram staining is done. The first stain is called Crystal violet. This is applied to the slide and left there for 30 seconds.This is then rinsed off and iodine is applied for 30 seconds. This is then rinsed off and acetone is applied for 6 - 10 seconds. This takes the colour off the surface of the cells so that the only stain that will be left will be any that has been allowed into the cell by Gram positive bacteria. This is then rinsed off and a red stain called safranin is applied for 30 seconds. This is basically a stain which will stick to the bacteria so that they will show up under the microscope. It will change the colour of the Gram negative bacteria to a pink colour because there is no darker purple dye retained within the cells.
Here is a diagram of the process:
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| Gram positive cocci |
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| Gram negative cocci |
You suit this look Jane! All seem really interesting your head must be swimming with all the new info.
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