Adhesion and invasion of Campylobacter jejuni in chickens with a modified gut microbiota due to antibiotic treatment

•Campylobacter jejuni is one of the major causative agents of human gastroenteritis in the developed world.•Historically, C. jejuni is considered as a commensal bacterium of chickens due to its mainly asymptomatic colonization of the chicken intestine.•We show that C. jejuni invades the cecum of antibiotic treated birds with limited gut microbiota and induces clinical signs and lesions.•These findings suggest C. jejuni to be a primary pathogen for chickens.•This study contributes to a better understanding of C. jejuni–host interaction. Campylobacter jejuni (C. jejuni) is a predominant cause of foodborne illness in humans, while its colonization in chickens is usually asymptomatic. Antibiotics are not routinely used to treat chickens against C. jejuni, but in the face of other bacterial diseases, C. jejuni may be exposed to antibiotics. In this study, chickens were treated with antibiotics (AT) to modify the gut microbiota composition and compared with untreated chickens (Conv) with respect to changes in C. jejuni-colonization and bacterial-intestine interaction. Groups of AT and Conv chickens were inoculated after an antibiotic-withdrawal time of eight days with one of three different C. jejuni isolates to identify possible strain variations. Significantly higher numbers of colony forming units of C. jejuni were detected in the cecal content of AT birds, with higher colonization rates in the spleen and liver compared to Conv birds independent of the inoculated strain (p < 0.05). Clinical signs and histopathological lesions were only observed in C. jejuni-inoculated AT birds. For the first time we demonstrated C. jejuni invasion of the cecal mucosa in AT chickens and its inter- and intracellular localization by using antigen-straining, and electronic microscopy. This study provides the first circumstantial evidence that antibiotic treatment with lasting modification of the microbiota may provide a suitable environment for C. jejuni invasion also in chickens which may subsequently increase the risk of C. jejuni-introduction into the food chain.