Campylobacter jejuni strains with different pathogenic potential shapes host-pathogen interactions and gut microbiota dynamics

Background Campylobacter jejuni is the leading cause of foodborne enteritis. Although typically a commensal of the avian gut, it can induce pro-inflammatory responses, damage intestinal integrity and affect broilers’ performance. To understand the host response to Campylobacter infection, ROSS 308 male broiler chickens were experimentally infected at 21 days of age with three C. jejuni strains of different pathogenic potential (potentially benign, potentially harmful and invasive). An unchallenged group served as control. Results After infection, feed conversion rate was significantly impaired by 3% in groups infected with the harmful and invasive strains. At 2-, 7- and 14-days post-infection (dpi), 10 birds per group were euthanized for Campylobacter isolation, evaluation of immune response, intestinal morphometry, microbiota composition and determination of short chain fatty acids. C. jejuni was recovered from all caeca samples from all infected groups and timepoints except for one infected bird at 2 dpi. At 7 dpi significant increase was observed in interferon gamma gene expression in chickens infected with the harmful and invasive strains, while bile secretory immunoglobulin A levels were elevated in all challenged groups. At this timepoint, chickens infected with harmful and invasive strains showed a reduced villus height:crypt depth ratio. Microbiota analysis revealed reduced α-diversity in infected birds, especially at 2 dpi. β-diversity showed distinct microbial clustering between control and infected groups at early timepoints, confirming infection-driven dysbiosis. Several differentially abundant genera were identified at early timepoints including enrichment of Faecalibacterium in controls, higher abundance of an unclassified Rikenellaceae genus in benign and invasive infected groups, and increased Clostridiales taxa at later timepoints in harmful and invasive infected groups. At early timepoints, infected chickens showed reduced butyrate and formate levels, along with increased lactate and succinate accumulation, particularly in chickens infected with the invasive strain. These metabolic changes reflect functional shifts in microbial activity associated with dysbiosis. Conclusions These results underscore the strain-specific pathogenic potential of C. jejuni in broilers, ranging from gut commensals to disruptors of intestinal integrity, highlighting the need for in-depth studies of Campylobacter biology for targeted control strategies, to improve animal health and control its spread to humans.