MacConkey Agar Base is a dehydrated culture medium formulated for the selective isolation and differentiation of Gram-negative bacteria, particularly those from the Enterobacteriaceae family. It is widely used in microbiology for analyzing various samples like clinical specimens, food, water, and dairy products. The medium contains ingredients that inhibit the growth of Gram-positive bacteria, while allowing Gram-negative bacteria to grow. Lactose fermenters produce pink colonies, while non-lactose fermenters form colorless or transparent colonies, aiding in differentiation.