Loss of crystal violet binding activity in stationary phase Yersinia enterocolitica following gamma irradiation

Ionizing radiation can eliminate virulent Yersinia enterocolitica from meat . It is possible, however unlikely, that a small number of Y. enterocolitic a could survive the pasteurization process. The virulence of Y. enterocolit ica is dependent upon the presence of a 70 kb plasmid. The effect of low-do se ionizing radiation on the plasmid-associated virulence trait of crystal violet binding was investigated. Y. enterocolitica strains which carried th e virulence plasmid were suspended in Butterfield's Phosphate Buffer or raw ground pork and irradiated to a dose of 1.0 or 1.25 kGy, respectively. Los s of crystal violet binding increased 10-fold following exposure to ionizin g radiation, regardless of the suspending medium. Polymerase chain reaction analysis of Y. enterocolitica isolates that did not bind crystal violet fo llowing irradiation indicated that loss of the virulence plasmid as opposed to mutation of a single plasmid-encoded gene, was the major mechanism for elimination of the crystal violet binding trait. (C) 2001 Academic Press.