HE Agar is a specialized medium designed for the selective isolation and culture of Salmonella and Shigella species. Through a dual mechanism of selective inhibition and a multi-pathogen biochemical chromogenic system, it enables Salmonella to form blue-green to blue colonies, often with a black center (due to hydrogen sulfide production). Shigella forms green, moist, raised colonies, while lactose-fermenting bacteria appear pink, enabling efficient identification.