Introduction Besides being very small, bacteria are also almost completely transparent, colorless and featureless in their natural states. However, staining can make the structures of bacteria more pronounced. The auxochrome imparts a positive or negative charge to the chromogen, thus ionizing it. The ionized stain is capable of binding to cell structures with opposite charges.
Basic stains bind to negatively charged cell structures like nucleic acids.
Methylene blue, crystal violet and carbolfuchsin are common basic stains. Acidic stains bind to positively charged cell structures like proteins. Picric acid, eosin and nigrosin are common acidic stains. In this exercise, we will use simple stains to show the general structures of some bacteria. Usually, a single basic stain is used in the procedure.