A modified crystal violet pectate (CVP) medium for detection and isolation of soft rot Erwinia spp. from plant materials

Abstract

A modified double-layer crystal violet-sodium polypectate medium for detection of soft rot Erwinia species from plant materials was developed and named CVPD. The basal and upper layer contained 0.6 and 0.3 % tryptone, respectively, to improve growth and cavity formation. The incorporation of 2,3,5-triphenylterrazolium chloride and L-asparagine in the basal medium and bromthymol blue in the upper layer resulted in pink to red colonies of the soft rot Erwinia species in addition to deep cavity formation while colonies of contaminating bacteria appeared white, red, green or yellowish without cavity formation. The addition of 3.2 muwg/ml and 0.8 mug/ml polymyxin B sulphate to the basal and upper layer medium, respectively, and 0.2 mg/ml SDS to the basal medium improved the selectivity and recovery of the pectolytic Erwinia spp. The recovery and selectivity of the medium was better than on the original CVPB medium prepared with Bulmer sodium polypectate.