Salmonella Typhimurium on XLD agar. Photo By: Carlos Rafael Manzano Palafox from Guadalajara Jalisco, México. – Xylose-Lysine Deoxycholate Agar (XLD Agar) is a selective medium recommended for the isolation and enumeration of Salmonella Typhi and other Salmonella species. – Red colonies, some with black centers. – The agar itself will turn red due to the presence of Salmonella type colonies.