Microbiology
Dyes or stains may be divided into two groups: basic and acidic. Basic dye : If the color portion of the dye resides in the positive ion , as in the above case, it is called a basic dye (examples: methylene blue, crystal violet, safranin). when using a basic dye , the positively charged color portion of the stain combines with the negatively charged bacterial cytoplasm (opposite charges attract) and the organism becomes directly stained (see Fig. 1) . Acidic dye : If the color portion is in the negatively charged ion , it is called an acidic dye (examples: nigrosin, congo red). An acidic dye , due to its chemical nature, reacts differently. Since the color portion of the dye is on the negative ion, it will not readily combine with the negatively charged bacterial cytoplasm (like charges repel). Instead, it forms a deposit around the organism , leaving the organism itself colorless (see Fig. 1) . Since the...