An enterotoxin-negative strain of Yersinia enterocolitica serotype O:3 is capable of producing diarrhea in mice.

A strain of Yersinia enterocolitica serotype O:3 that consistently produced heat-stable enterotoxin at 22 but not at 37 degrees C and another strain of the same serotype which did not produce enterotoxin at 22 degrees C were both positive for autoagglutination at 35 degrees C, a test that has been related to virulence in yersiniae. Both strains were infective for HeLa cells and produced guinea pig conjunctivitis. Mice infected with either strain through their drinking water developed diarrhea and excreted the organism in high numbers in the feces. A control strain of serotype O:3 positive for enterotoxin and HeLa cell infectivity but negative for autoagglutination was avirulent. Extracts of feces and intestines from mice with diarrhea were negative for enterotoxin. The results indicate that the heat-stable enterotoxin produced in vitro by some strains of Y. enterocolitica and measured by the infant mouse assay plays no role in pathogenesis as described by the mouse diarrhea model.