Elimination of Yersinia enterocolitica by chlorine on fresh tomatoes

The effect of temperature throughout 18 day-storage and the efficacy of different free chlorine concentrations in washing solutions upon the survival of Yersinia enterocolitica on surface of inoculated fresh tomatoes were studied. Two virulence plasmid-bearing strains. A. Y. enterocolitica W1024 0:9--a reference strain--and B. Y. enterocolitica B1 0:5 Lis Xz--a strain isolated from food in San Luis, Argentina, were assayed. Counts of both strains at 6 degrees C did not present significant changes during the first 4 days, but increased until day 15. Both strains were able to grow on tomatoes stored at 22 degrees C and 35 degrees C. At 22 degrees C maximum values were obtained on days 3 and 4, with a subsequent significant decrease. Highest counts were obtained at 37 degrees C. No detectable levels of viable cells were observed by using 500 ppm free chlorine washing solution. Non-inoculated tomatoes were analyzed for Y. enterocolitica with negative results. Zero tolerance for pathogenic Y. enterocolitica strains has been recommended for ready-to-use vegetables. Therefore, sanitary measures should be taken in the manipulation and storage of fresh tomatoes.