ATTEMPTS TO FIND PHENOTYPIC MARKERS OF THE VIRULENCE PLASMID OF RHODOCOCCUS-EQUI

Four isolates of Rhodococcus equi, from pneumonic foals, and containin g the 85 kb virulence plasmid, a porcine isolate containing an 80 kb p lasmid, and their plasmid cured derivatives, were examined for 239 phe notypic properties in an attempt to find characters other than the vir ulence-associated protein (VapA) which might be encoded by the virulen ce plasmid in organisms grown at 37 degrees C. Tests chosen included t hose which have previously given variable results for R. equi isolates , since such variability might be attributed to plasmid curing, and ch aracteristics which have been described as properties of plasmids of R hodococcus species other than R. equi. Tests included cadmium resistan ce, Congo red binding, resistance to 26 antibiotics, conventional clin ical microbiological tests, utilization of 95 different carbon sources , enzymatic activities in API ZYM, fluorogenic assays for exo- and end opeptidase, glycosidase activities, and testosterone degradation. Apar t from production of VapA by foal isolates, no phenotypic property was identified in the plasmid-positive isolates. Phenotypic characteristi cs of R. equi that have not been described before, and might be useful in identification were: metabolism of N-acetyl-beta D-glucopyranoside , alpha- and beta-hydroxybutyric, alpha-ketobutyric and N-acetyl-gluta mic acids, of methylpyruvate, heptanoate, nonanoate and stearate ester s; exopeptidase activity against alanine-alanine-tyrosine, alanine-phe nylalanine-lysine, glycine-arginine, lysine-alanine, and valine-glycin e-alanine; endopeptidase activity against arginine and methionine; and hydrolysis of bis-phosphate ester.