Influence of the virulence plasmid and the Congo red reaction on the antimicrobial susceptibility of yersinia species

Abstract

Seventeen strains of Yersinia enterocolitica and related species were examined for their susceptibility to a variety of antimicrobial agents. Twelve of the strains were clinical isolates which carried a virulence plasmid; five were food isolates which lacked plasmids. When grown on agar containing Congo red or haemin, each strain yielded pigmented (CR+) and non-pigmented (CR-) variants. CR+ bacteria of clinical origin were virulent, whereas CR+ food isolates and all CR- bacteria were avirulent. The susceptibility of CR+ and CR- bacteria to the following agents was compared: ampicillin, chloramphenicol, latamoxef, nalidixic acid, novobiocin, polymyxin B, rifampicin, streptomycin, tetracycline..