MacConkey Agar is a selective and differential culture medium primarily used in microbiology laboratories to isolate and differentiate gram-negative bacteria, particularly Enterobacteriaceae and other lactose-fermenting organisms. It contains **** violet and bile salts, which inhibit the growth of gram-positive bacteria while allowing the growth of gram-negative bacteria. Additionally, the medium contains lactose and a pH indicator (neutral red), which differentiate lactose fermenters (pink colonies) from non-lactose fermenters (colorless colonies). MacConkey Agar aids in the identification and isolation of pathogens, especially in clinical specimens.