Because a protective outer capsule does not absorb most basic dyes, a negative staining technique is typically used for capsule staining to determine if cells in a specimen are encapsulated, which serves as an important diagnostic tool for evaluating a microbe's virulence. In a negative capsule stain, a dye such as India ink or nigrosin colors the background without penetrating the capsule, leaving a visible clear halo around each cell without requiring the specimen to be heat-fixed. Alternatively, a combination of positive and negative staining techniques can be used, where a positive stain colors the body of the cell and the negative stain colors the background, rendering the capsule as a clear halo.

Capsule Stain

Bacterial specimens interact with dyes, such as Indian ink or nigrosin, which produce a colored background where the unstained bacteria are easily observed. Slender structures, such as spirochetes, can be viewed with negative staining.

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Due to the lack of contrast in light microscopes, observation of structural details in live bacteria is not possible. Staining specimens adds contrast to the image. This involves dying and fixing the specimen, subsequently killing the bacteria. Commonly used staining techniques are:
- Simple Stains
- Negative Staining
- Impregnation Methods
- Differential Stains

Stained Preparations

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Differential stains add different colors to bacterial structures. 
Two most common differential stains are the gram stain, developed by Christian Gram as a method of staining bacteria in tissues, and the acid fast stain 

Differential Stains

Methylene blue or fuchsin dyes are required for simple staining procedures. While adding the same color to bacterial specimens, they provide color contrast. 

Simple Stains

Negative Staining

The addition of silver to the surface of bacteria may allow researchers to view thinner cellular structures that cannot be observed with ordinary microscopy. Impregnation methods are used to demonstrate spirochetes and bacterial flagella.

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