What is the most common bacteriology stain used in laboratories?

The Gram stain is considered the most common bacteriological stain used in laboratories. This staining method, developed by Hans Christian Gram, is crucial for differentiating bacterial species into two large groups based on the properties of their cell walls: Gram-positive and Gram-negative.

The Gram stain involves a series of steps, including the application of crystal violet dye, followed by iodine, which binds the dye, and then decolorization with alcohol or acetone. Finally, it is counterstained with safranin. The outcome of this procedure provides essential information: Gram-positive bacteria retain the crystal violet dye and appear purple, while Gram-negative bacteria do not and take up the safranin, appearing pink.

This distinction not only aids in the identification and classification of bacteria but also in determining appropriate antibiotic treatments. The Gram stain is thus indispensable in diagnostic microbiology due to its speed, simplicity, and the critical information it conveys about bacterial structure that influences clinical decision-making. Other stains mentioned in the options are used for specific purposes, such as identifying mycobacteria (acid-fast stain) or highlighting cell structures, but none have the broad utility and significance of the Gram stain in routine laboratory settings.