Gram stain is a critical 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. This differentiation helps in the identification and selection of appropriate antibiotics for treatment. In clinical settings, Gram staining is often the first step in diagnosing bacterial infections, such as pneumonia, urinary tract infections, and sepsis, allowing for rapid preliminary identification of the causative organism. It is widely used in hospitals and laboratories due to its speed, simplicity, and cost-effectiveness. The results guide initial antimicrobial therapy while waiting for more definitive culture or molecular test results. Additionally, Gram stain is used in research to monitor bacterial cultures and assess the purity of samples.