24 Jun

Simple Stain

Using a single stain to color a bacterial cell is commonly referred to as a simple stain.  The most common dyes for this type of stain are methylene blue, fuchsin, and crystal violet.  These dyes work well because they have positively charged color bearing ions or chromophores.  Bacteria are negatively charged which creates a natural attraction with positively charged dyes.  Basic or cationic dyes have a positive charge making them practical for bacterial staining whereas acidic dyes like eosin have a negative charge.  Dyes such as eosin will not stain bacterial cells due to their repelling forces.  Staining times for most simple stains are relatively short, usually from 30 seconds to 2 minutes, depending on the affinity of the dye.  After a smear has been stained for the required time, it is washed off gently, blotted dry, and examined directly under oil immersion.  This type of slide is useful in determining basic morphology and the presence or absence of certain kinds of granules.  pauln