Arsenic is one of the most important global environmental pollutants. In the present study, fifty one clinical strains of Yersinia enterocolitica biovar 1A showed high resistance to arsenite and arsenate. The minimum inhibitory concentration (MIC) of arsenite (0.625-20 mM) was lower than arsenate (10-80 mM). Growth of Y. enterocolitica in 2 mM arsenite led to 2-8 fold increase in MICs of the five antibiotics (amikacin, ciprofloxacin, gentamycin, kanamycin and tetracycline), suggesting expression of arsenite-induced multiple antibiotic resistance among the strains. Proteomic analysis of Y. enterocolitica revealed differential expression of certain proteins following arsenite exposure, which included a putative outer membrane porin (OmpA) and a putative amino acid transporter protein. In conclusion, modulation of membrane permeability may be involved in the induction of arsenite-mediated expression of multiple antibiotic resistance in Y. enterocolitica. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).