The most common method to increase contrast is to stain part or all of the microbe. Nonspecific stains will react with all microbes in an identical fashion. They are useful solely for increasing contrast so that morphology, size and arrangement of organisms can be determined.
Specific stains give varying results depending on the organism being treated.
These results are often helpful in identifying the microbe. How Stains Work Stains are chemicals containing chromophores , groups that impart color. Their specificity is determined by their chemical structure. The surface of bacteria at neutral pH is somewhat negatively charged and will therefore attract basic dyes. Some examples of basic dyes are crystal violet, safranin, basic fuchsin and methylene blue .