Practical lectures continue in the branches of the General Sciences Department in the College of Basic Education, where they took place in the Laboratory of Differential Staining, in which the Gaam stain is used, and it is considered one of the most important and most common dyes in microbiology laboratories and its importance lies in its effectiveness in terms of its use in diagnosing Bacteria, especially since it cannot be applied to some microorganisms, such as primitives and fungi, except for yeasts, as they are positive for the cram stain.
Staining of bacteria with a cream stain:
This method was discovered by Hans Christian Kram 1884 A.D. when he noticed that bacteria lose the color of the pigment when disposing of the excess amount of it. This method is used in the diagnosis and classification of bacteria.
The bacteria, according to the pigmentation, are divided into two groups:
1 – Gram positive bacteria
They appear under the microscope in violet color and Cram-negative bacteria appear under the microscope in pink-red color The difference between the positive and negative characteristics depends on the components of the cell wall of the bacteria
The method of work :
1- A crystal vioet dye (base dye) is added for a minute
The fixed sample is then washed with water, where the bacteria capable of absorbing it are stained
2- Add the dilute iodine solution solution Iodine for this one minute
The solution reduces the solubility of the crystal violet dye inside the cell by its association with the dye to form ionic bonds between the dye and iodine.
3- Add Ethanol or Aceton (95%) for half a minute, then wash it with water to remove the dye complex and iodine.
4- Add Safranin dye (secondary dye) for half a minute, then wash it with water
5- Dry the slice with air or with a drying paper and examine under a microscope
The cream dye mechanism:
1- The bacteria differ in their acceptance of the primary and secondary dye
2- The Gram-positive bacterial cell wall is thicker than the cell wall
Negative chemical composition of the chromium stain.
