GRAMSTAIN

The Gram stain is a pivotal microbiological test used to categorize bacteria into two main groups: Gram-positive and Gram-negative. By applying a purple stain to a bacterial sample, the subsequent color reaction—either retaining the purple stain (Gram-positive) or taking up a pink or red counterstain (Gram-negative)—provides crucial information about the bacteria’s cell wall composition. Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus, possess a thick peptidoglycan layer, while Gram-negative bacteria, including Escherichia coli and Salmonella, have a thinner peptidoglycan layer and an outer membrane. , as Gram-positive and Gram-negative bacteria respond differently to various antimicrobial agents.