A negative stain is a dye that colors the background rather than the biological specimen itself. By leaving the specimen unstained and producing a dark background, this technique creates a silhouette effect where light cells stand out prominently. Common examples of negative stains include India ink and nigrosin.

Negative Stain

An acidic stain is a dye that colors positively charged molecules and structures, such as proteins. Depending on the specific chemistry of the bacterial cell, acidic stains can function as either positive or negative stains. Examples of acidic stains include eosin, acid fuchsin, rose Bengal, and Congo red.

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In simple staining, a single dye is applied to a specimen to emphasize particular structures. This technique generally causes all of the organisms in a sample to appear uniformly as the same color, even if the sample contains multiple types of organisms, making it useful for basic visualization but not for differentiation.

Simple Stain

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A basic stain is a positively charged dye that colors negatively charged molecules and structures, such as nucleic acids and proteins. Examples of basic stains include methylene blue, crystal violet, malachite green, basic fuchsin, carbolfuchsin, and safranin. Because the dye is attracted to the cell, the outcome of this positive stain is dark cells visible against a light background.

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