xlt agar xlt agar xlt agar (xylose lysine tergitol-4) is a selective culture medium for the isolation and identification of salmonellae from food and environmental samples. it is similar to xld agar; however, the agar is supplemented with the surfactant, tergitol 4, which causes inhibition of proteus spp. and other non-salmonellae. successful growth of salmonella will result in growth of red colonies with a black centre. xlt agar contains: proteose peptone 1.6g/l yeast extract 3g/l l-lysine 5g/l xylose 3.75g/l lactose 7.5g/l sucrose 7.5g/l sodium chloride 5g/l sodium thiosulphate 6.8g/l ferric ammonium citrate 0.8 mg/l phenol red 0.08g/l agar 18g/l tergitol-4 4.6ml/l