Tween Media for Semiselective Isolation ofXanthomonas campestrispv.vesicatoriafrom Soil and Plant Material

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Abstract
Three semiselective culture media have been developed for the isolation of Xanthomonas campestris pv. vesicatoria (X. c. pv. vesicatoria) from soil and plant material. These media contain Bacto peptone, Tween 80, potassium bromide, calcium chloride, and Difco agar. Selectivity is afforded through the use of boric acid, methyl green, and the antibiotics cephalexin, 5-fluorouracil, tobramycin, and cycloheximide. Although elimination of contaminating bacteria is not total, identification of Xanthomonas is aided by the use of Tween 80, a fatty acid ester and substrate for lipolytic enzymes of the pathogen. The released fatty acids are precipitated by calcium and form soap crystals around the colonies. Also, production by Xanthomonas of a yellow pigment, a dibromomethoxyphenyl polyene, is enhanced by incorporating KBr into the media. The resulting colonies of Xanthomonas have a fried-egg appearance. Compared with King''s medium B, recovery on Tween media of X. c. pv. vesicatoria averages more than 90%, as does reduction of contaminating microorganisms from soil and plant samples.