> See also: > - [[Analytical Microbiology Techniques.canvas|Analytical Microbiology Techniques]] # Cellular Staining Cell samples can be stained using specific dyes to make it easier to analyze them using a bright field microscope by adding contrast. The technique is useful for identifying *morphology (shape), size, and arrangement* of the sample/ ## Staining Reagents Primary Stain Mordant - A substance, typically an inorganic oxide, that *combines with a dye* or stain and thereby *fixes it in a material* Decolorizer Counter-stain ### Types of Dyes **Cationic:** [[Acids and Bases|Basic]] dyes, positively charged chromophores - Positive (+) ions will exhibit color - Will be attracted to the net-negative charge of bacterial cells - *Ex: methylene blue, crystal violet* **Anionic:** [[Acids and Bases|Acidic]] dyes, negatively charged chromophores - Negative (-) ions will exhibit color - Will be repelled by the negative charge of bacterial cells, allowing the background to take on a color while the cell samples remain unstained. This technique is often referred to as *negative staining*. - *Ex: acid fuchsin, congo red, nigrosin (black anionic dye)* ## Staining Techniques There are several major types of staining techniques: 1. **Simple Stains:** Using a single dye to stain all cells present - Typically use a *cationic dye* that binds to negatively charged plasma membranes of cells 2. **Negative Stains:** The dye is used to stain the background rather than the cells themselves (“stars in a night sky”) 3. **Differential Stains:** Differentiate microbes or bacteria based on certain characteristics (Ex: Gram Staining) 4. **Structural Stains:** (Ex: Endospore)