Slide Preparation: Direct Stain

Microbial cells are small and transparent. Stains are often used to increase contrast between the cells and the background, making them easier to see under the microscope. Since many of the cell components are negatively charged, stains with positively charged chromophores (the colored ion of the dye) will attach to the cells. Examples of such stains include methylene blue, crystal violet, and carbol fuchsin.

  • Make a heat-fixed smear, taking care not to use too much culture if working from an agar culture.
  • Place the slide on a staining rack over a sink or catch basin.
  • Add a drop of dye to the smear. You need enough stain to just cover the smear, not the whole slide.
  • Allow the dye to act. (One minute is generally adequate.)
  • Gently rinse the dye from the slide with water from a squirt bottle.
  • Gently blot the slide and observe under the microscope.

Take the Quiz

On to Aseptic Techniques