These bacterial cells possess chemical structures with acidic protoplasm and a thick peptidoglycan layer. Techoic acids, intertwined among peptidoglycan and techoic acids, are the prominent surface antigen determinants. 

Gram Positive Cells

Gram negative cells, rich in lipids, have cellular membranes composed of phospholipids, proteins and lipopolysaccharides (LPS). Gram negative cells have a thin peptidoglycan layer without teichoic acids. The outer membrane has lipopolysaccharide channels that transport solutes. Lipoproteins cross link the outer membrane and the peptidoglycan layer. 

Gram Negative Cells

Reactions to gram stains relates to the permeability of the cell wall and cytoplasmic membrane to the iodine complex. Gram negative cells permit the outflow of this dye complex during the removal of the stain. Gram staining is an essential procedure to differentiate bacteria and study morphological bacterial structures. 

Gram Stains

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 

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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

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

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.

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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