Effect of salt and acidic pH on the stability of virulence plasmid (pYV) in Yersinia enterocolitica and expression of virulence-associated characteristics

The stability of the Yersinia enterocolitica virulence plasmid (pYV) under different NaCl concentrations and under acidic pH conditions was investigated. Exposure of five strains representing five serotypes of pYV-bearing virulent Y. enterocolitica to 0.5, 2 and 5% NaCl and under conditions of pH 4, 5, and 6 for 24 h at 28 °C in the stationary phase did not lead to the loss of the virulent pYV from the surviving cells. At pH 3.0, the cells did not survive. Virulence assays using crystal violet binding, low-calcium response, Congo red-uptake, hydrophobicity by latex particle agglutination, and autoagglutination, as well as PCR assay to determine the presence of pYV indicated that the surviving cells were still virulent.