The role and interaction of gut microflora and local immune response in Campylobacter jejuni infection in chicken

Chicken is regarded as the main reservior for Campylobacter jejuni (C. jejuni)-induced gastroenteritis in humans worldwide. C. jejuni may colonize in most cases the chicken intestine asymptomatically without significant macroscopical and microscopical lesions. Little is known about the interaction between C. jejuni and the chicken host, which may be significantly affected by the genotype, the maturation stage of the chicken immune system and the developing gut microflora composition. The aim of this study was to investigate the influence of age, genotype and feed on C. jejuni colonization pattern and immunological reactions in chickens. In the first study, host immune responses as well as gut microflora composition were compared between broiler chicken, which had been inoculated with one of two different C. jejuni strains (Lior6 or 0097) at different days post hatch (dph) including one, 10, 22 and 31 dph. The highest C. jejuni-colonization rate and numbers of colony forming units (CFU) were detected in caecal content of birds inoculated at one dph. While the birds inoculated at 22 dph showed the lowest CFU compared to the other three age groups (p < 0.05) independent of the inoculated C. jejuni-strain. Interestingly, the most prominent immune reactions were induced in birds, which had been C. jejuni-inoculated at one and 22 dph. We observed in these C. jejuni-inoculated age groups a significant upregulation of CD4+, CD8+T lymphocytes and B-cells in the lamina propria (LPL) as well as of CD4+ intraepithelial lymphocytes (IEL) in either caecum or ileum in comparison to their control hatch mates (p < 0.05). No changes were seen in birds which had been C. jejuni-inoculated at 10 or 31 dph. This increase in numbers of immune cells in the gut of these C. jejuni-inoculated age groups was accompanied by upregulation of mRNA-expression of interferon (IFN)-γ and the chicken interleukin (IL)-8-homolog at seven dpi compared to control birds of the same age group (p < 0.05). In addition, age had a visible effect on the gut flora composition comparing eight and 29 day old chickens and it influenced C. jejuni-induced changes in the microflora. Based on the results of our first study, C. jejuni strain Lior6 and two age groups, one and 22 dph, were selected to conduct the second study, in which the role of genetic background and feed on C. jejuni colonization, immune response and gut microflora composition was investigated. Broiler-type (BT) and layer-type (LT) birds fed with either commercial broiler feed (bf) or layer feed (lf) were inoculated with C. jejuni at day one or day 22 dph. Lower colonization rates and numbers of CFU of C. jejuni were observed in birds, which had been C. jejuni-inoculated at 22 dph compared to birds inoculated at one dph independent of genotype and diet. Birds fed with bf showed higher numbers of CFU of C. jejuni compared to lf-fed groups independent of genotype. C. jejuni colonization significantly influenced T and B lymphocyte numbers and cytokine expression levels in caecum of BT birds independent of diet, this effect was detectable in LT birds. Diet had an effect on gut microflora composition in both BT and LT birds. The gut microflora composition was changed after C. jejuni-inoculation and this change varied between both genotypes. Overall, this research demonstrates that C. jejuni-colonization pattern and immune response to C. jejuni are significantly influenced by age, genotype of chicken and diet. The evolving gut microflora may also be involved in these influences, and in addition may be affected by C. jejuni colonization. Therefore, this project contributes to the understanding of C. jejuni-host interaction. It provides the basis for further investigations on the interaction of host and gut microflora in association with colonizing pathogens.