Simple Stains

Negative Stain--uses an acidic dye which stains the background but leaves the cells unstained

This is a negative stain of Staphylococcus aureus

This is a negative stain of Klebsiella pneumoniae

Negative stains are useful in determining cell morphology.  The slide is not heat-fixed which reduces the probability that the cells will shrivel or shrink resulting in distorted morphology.

Differential Stains

The Gram stain is one of the most useful procedures in microbiology.

  Staphylococcus aureus (Gram stain)

Note the purple color of the Gram (+) coccus.  Also note the grape-like clusters of cells.