Gram Staining

A gram stained smear is a key diagnostic tool that aids in the preliminary diagnosis of infectious agents in a clinical microbiology laboratory. This differential stain is based on the cell wall differences of gram positive and gram negative bacteria. Gram stain can detect the presence of microorganisms in a patient specimen and also can be employed in identifying microbes from a culture. All clinically important bacteria can be identified using the gram stain with the exception of intracellular bacteria such as Chlamydia, those that lack cell wall such as Mycoplasma and those organisms that cannot be resolved by light microscopy such as spirochetes.
The challenge is fourfold: To prepare a bacterial smear for Gram staining, to perform the Gram staining procedure, to identify the shape and gram reaction of the bacteria, and to evaluate the quality of the stain.