A DIFFERENTIAL MEDIUM FOR SEMISELECTIVE ISOLATION OF XANTHOMONAS-CAMPESTRIS PV VESICATORIA AND OTHER CELLULOLYTIC XANTHOMONADS FROM VARIOUS NATURAL SOURCES

A semiselective medium (CMC-E) was more effective than Tween medium B agar or nutrient agar for recovery of Xanthomonas campestris pv. vesicatoria from the environment or plant material. The selectivity of CMC-E medium was from the sodium salt of high-viscosity carboxymethyl cellulose as the primary carbon source and gelatin as the sole source of nitrogen. Additional selectivity was from the incorporation of eosin Y, methylene blue, bacitracin, cephalexin, cycloheximide, 5-fluorouracil, neomycin sulfate, and tobramycin. Colonies of cellulolytic Xanthomonas spp. on CMC-E were circular, flat, reddish purple, and distinct from those of most other bacterial species because they were in the center of saucer-shaped pits formed in the carboxymethyl cellulose-agar gel. Plating efficiencies for strains of Xanthomonas on CMC-E varied from 0 to 111%, but for most strains, the efficiencies were high enough to permit quantitative studies. By use of CMC-E, X. c. vesicatoria was recovered from pepper seed, irrigation water, and air samples.