Experimental pig yersiniosis to assess attenuation of Yersinia enterocolitica O:8 mutant strains.

An experimental oral pig model was used to assess the pathogenic and immunogenic potential of Yersinia enterocolitica serotype O:8 wild-type strain 8081-L2 and its lipopolysaccharide (LPS) mutant derivatives: a spontaneous rough mutant 8081-R2, strain 8081-DeltawzzGB expressing O-antigen with uncontrolled chain lengths, and strain 8081-wbcEGB expressing semirough LPS with only one O-unit. Microbiological and immunological parameters of the infected pigs were followed from day 7 to 60 postinfection. The wild-type and all LPS mutant strains persisted in the lymphoid tissue of tonsils and small intestines, causing asymptomatic infection without any pathological changes. Although the pig is known as a reservoir of Yersiniae, a precise analysis of pathogenic and immunogenic parameters based on different in vitro tests (hematological response, killing ability of leukocytes and blood sera, antibody response, hydrogen peroxide production by macrophages, classical and alternative pathways of complement activation), revealed significant attenuation in the pathogenicity of the LPS mutant strains but not the loss of immunogenic potential. In comparison with the other strains, strain 8081-DeltawzzGB demonstrated more continuous leucocytosis with monocytosis, higher invasive potential, significant activation of hydrogen peroxide production by macrophages and an effective immunoglobulin G immune response accompanied by relevant histological immunomorphological rearrangements.

Comparison of the course of infection of virulent Yersinia enterocolitica serotype O:8 with an isogenic sodA mutant in the peroral rabbit model.

Peroral infections of rabbits with a virulent Yersinia enterocolitica serotype O:8 wild-type strain (WA-314) and its isogenic Mn-cofactored superoxide dismutase (sodA) mutant were analyzed with respect to the following parameters: clinical findings, bacterial ability to colonize and persist in different tissues, bacterial resistance to the killing effect of leukocytes and blood sera, IgG antibody response, pathomorphological and immunomorphological changes. In comparison to WA-314, the sodA mutant was markedly impaired in its ability to disseminate into the brain and viscera, and to cause hyperthermia, leukocytosis with monocytosis, granulocytosis and initial lymphopenia. The sodA mutant strain was more susceptible to bactericidal activity of leukocytes and blood sera than the parent strain WA-314. Moreover, in comparison to WA-314, the sodA mutant was attenuated for mice after oral, intravenous, and intraperitoneal inoculation and totally avirulent for rats. Strikingly, the sodA mutation led not only to attenuation of virulence but also enhanced immunogenicity (as reflected by the specific antibody response). These features are consistent with the mild immunomorphological changes observed after infection with the sodA mutant as compared to the severe tissue lesions caused by the virulent strain WA-314. In conclusion, this study demonstrates that the sodA mutation in Y. enterocolitica leads to loss of virulence and gain of immunogenicity in rabbits. These are promising features for a live oral vaccine carrier strain.