Gram stain is not a single chemical but a staining technique used in microbiology to classify bacteria into two groups—Gram-positive and Gram-negative—based on the physical and chemical properties of their cell walls. The method involves a series of reagents applied to a bacterial sample, including crystal violet (primary stain), iodine (mordant), alcohol or acetone (decolorizer), and safranin (counterstain).

The primary application of the Gram staining technique is in clinical diagnostics and microbiology laboratories. It allows rapid preliminary identification of bacteria from patient samples such as blood, urine, cerebrospinal fluid, or wound swabs. This classification guides initial antibiotic therapy, as Gram-positive and Gram-negative bacteria differ in their susceptibility to various antibiotics.

In research settings, Gram staining helps in characterizing bacterial cultures during isolation and identification processes. It is also used in quality control in pharmaceutical and food industries to detect bacterial contamination.

Due to its simplicity, speed, and cost-effectiveness, Gram stain remains a fundamental tool in both medical and industrial microbiology.