Serum resistance associated with virulence in Yersinia enterocolitica.

Yersinia enterocolitica strains that exhibited a calcium requirement for growth and autoagglutination at 37 degrees C were invariably virulent in rabbits, causing diarrhea and a high degree of lethality, and were capable of colonizing the intestinal lumen and establishing foci of infection on the Peyer's patches of mice. Strains that had lost the properties of calcium dependency and autoagglutinability were totally avirulent in rabbits and were quickly eliminated from the intestinal lumen and tissues of mice. Virulent and avirulent strains were shown to be equally invasive to HeLa cells. However, the virulent strains were resistant to the bactericidal action of normal serum, and this serum resistance was lost with the loss of virulence. Furthermore, the serum resistance of virulent strains was expressed, as were other properties, when strains were grown at 37 degrees C, but not at 27 degrees C. These results suggest that a virulence factor associated with serum resistance plays an essential role in the pathogenicity of Y. enterocolitica.