XLT4 Agar is primarily used in microbiology for the selective isolation and differentiation of Salmonella species from clinical, food, and environmental samples. It supports the growth of Salmonella while inhibiting the growth of non-target organisms such as Gram-positive bacteria and some non-Salmonella Gram-negative species. The medium contains selective agents and indicators that allow Salmonella to appear as distinctive black colonies due to hydrogen sulfide (H₂S) production, often surrounded by a red or pink halo, aiding in presumptive identification. This makes XLT4 Agar a valuable tool in diagnostic laboratories and food safety testing where rapid and accurate detection of Salmonella is critical.