Experimental Pathogenicity of Recent North American Isolates of Yersinia enterocolitica

Two isolates of Yersinia enterocolitica recently found in humans in North America and one isolate of flea origin killed mice after sc inoculation. Median lethal doses varied from 1.6 × 104 to 54 × 104 bacteria. Of 11 remaining isolates tested in mice, all but four produced distinct morbidity without extensive mortality. The LD50 after ip inoculation was 1,000-fold less than after sc inoculation into mice. One selected isolate was also tested in gerbils. All gerbils inoculated ip with as few as 250 organisms died within four days. These findings indicate that this bacterial species can no longer be considered to be nonlethal for laboratory animals. Studies of the pathology and immunopathology of Y. Enterocolitica disease processes, which were previously impractical because of the lack of suitable susceptible experimental animals, are now possible.