Experimental pig yersiniosis to assess attenuation ofYersinia enterocoliticaO:8 mutant strains

Abstract

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-DwzzGB 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-DwzzGB 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.

Essential Role of Invasin for Colonization and Persistence of Yersinia enterocolitica in Its Natural Reservoir Host, the Pig

“…In one single study, employing an experimental oral pig model, a conventional large breed was used to assess the pathogenic potential of a restriction-deficient (R Ϫ M ϩ ) derivative of strain O:8 8081v. Similar to the minipig model in this study, the 8081v derivative persisted mainly in the lymphoid tissues of the tonsils, and no bacteria were detected in the small intestine on day 7 postinfection (19). Challenge with a 500-fold-higher dose of bacteria also caused asymptomatic infections without major pathological signs in larger-breed pigs, and only a very slight enteric catarrhalic inflammation was detectable early during infection (19).…”

“…Challenge with a 500-fold-higher dose of bacteria also caused asymptomatic infections without major pathological signs in larger-breed pigs, and only a very slight enteric catarrhalic inflammation was detectable early during infection (19). However, several histological changes were observed in the brain (meningoencephalitits), lung (pneumonia catarrhalia), liver (lymphohistiocytic nodules), and several other tissues (hyperplasia of lymph follicles in the small intestine and the mesenteric lymph nodes) between days 14 and 45 postinfection (19).…”

“…In particular, O:3 strains, the most frequent source of human infections, can be routinely isolated from pigs, which are usually symptomless carriers (1,15,16). Pigs can carry these pathogens for long time periods in the oropharynx (tonsils) and the intestinal tract without any clinical signs, leading to a prevalence of 35% to 70% in fattening pig herds (17)(18)(19). As a consequence, outbreaks of yersiniosis are mostly associated with the consumption of raw or undercooked pork or pork products (e.g., chitterlings) (18,20,21).…”

Human and Animal Isolates of Yersinia enterocolitica Show Significant Serotype-Specific Colonization and Host-Specific Immune Defense Properties

“…Infected macrophages were fixed with 2.5% glutaraldehyde and 2% tannin, washed with cacodylate buffer, and fixed with 1% aqueous osmium for 1 h at room temperature. Dehydration was achieved with a graded series of acetone (10,30, and 50%) on ice. At 70% dehydration, samples were incubated overnight in 70% acetone and 2% uranyl acetate and dehydrated with 90% and 100% acetone on ice.…”

“…Pathogenic Y. enterocolitica carriage rates in swine range from 35% to 70% of herds and 4.5% to 100% of individual swine (8). The bacteria colonize their oropharynx, nasopharynx, and intestinal tract for long periods without induction of pathological changes (9,10).…”