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Microbiology: Stains, part 1.

A stain is an organic compound composed of:

  • Benzene ring: organic colorless solvent.
  • Chromophore: the color component.
  • Chromogen = benzene component + chromophore component.
  • Auxochrome: helps to modify the chromophore’s ability to absorb light; and modifies the chromogen (ionization) to help it bind to tissue/fibers.

Acidic stains: Sodium, potassium, calcium or ammonium salts ionize such that chromogen has anionic properties and has affinity for the “positive” components of a cell (e.g. picric acid).

Basic stains: Chlorides or sulfate salts of colored bases ionize such that chromogen has cationic properties and has affinity for the “negative” components of a cell (methylene blue).

Differential stains: are more complex, use 2 contrasting stains, and help to separate organisms/cells; and/or help to visualize structures such as flagella, capsule, spore, or nucleus.

Reference

Cappuccino, J. G., & Welsh, C. (2018). Microbiology: A laboratory manual.