SS Agar is a specialized medium designed for the selective isolation and culture of Salmonella and Shigella species. Through the dual action of a selective inhibition mechanism and a chromogenic identification system, it enables non-lactose-fermenting Salmonella and Shigella to form colorless, transparent colonies, Hydrogen sulfide-producing strains exhibit a central black zone, while lactose-fermenting bacteria (such as Escherichia coli) form red colonies, enabling efficient differentiation.