Arsenic and cadmium resistance in environmental isolates of Yersinia enterocolitica and Yersinia intermedia

Environmental strains of Yersinia enterocolitica representing biotype 1A lack virulence plasmid (pYV) and are regarded as non-pathogenic. Though these occupy a diverse range of environmental niches, nothing is known about their resistance to heavy metals. The minimal inhibitory concentrations (MICs) of various metal ions, namely Ag+, Cu2+, Zn2+, Cd2+, As5+, and As3+, for strains of Yersinia enterocolitica (biotype 1A) and Yersinia intermedia (biotypes 1, 2, and 4), isolated from sewage effluents or pork, were determined. All isolates were resistant (MICs 2.5-5 mM) to Cd2+. The MICs of arsenic varied with bacterial strain and the chemical species of the arsenic used. For the majority of the strains, however, it was between 5-10 mM of Na2HAsO4.7H2O and NaAsO2, and 0.625-2.5 mM of As2O3. Except for one isolate, MICs of Ag+, Cu2+, and Zn2+ for these strains were in the range of 0.3-0.625 mM.