A new semi-selective medium for Xanthomonas campestris pv. vitians, the causal agent of bacterial leaf spot of lettuce

A semi-selective medium containing maltose, methyl green, and antibiotics ( MMG) was developed for the isolation of Xanthomonas campestris pv. vitians. The semi-selective medium was evaluated based on plating efficiency of X. campestris pv. vitians in cell suspensions of pure cultures from leaves and soil. MMG medium allowed recovery of 5.7 to 30.6% of the X. campestris pv. vitians colonies recovered on nutrient agar and 0.1 to 8.4% of those recov ered on 1/10-strength tryptic soy agar. MMG inhibited growth of most backgr ound bacteria and allowed reliable identification of X. campestris pv. viti ans. The semi-selective medium contained (per liter) maltose (10 g), trypto ne (5 g), K2HPO4 (3.5 g), KH2PO4 (2.75 g), trace elements (0.02 to 1.0 mg), methyl green (2 mi of a 1% aqueous solution), amoxicillin (32 mg), cephalo thin (32 mg), cycloheximide (50 mg), and agar (15 g).