Analysis of Bacterial-Host Interactions Between Campylobacter jejuni and the Avian Host During Commensalism
Bingham-Ramos, Lacey Kathleen
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Campylobacter jejuni is a leading cause of bacterial enteritis in humans throughout the world. In contrast to the disease seen in humans upon infection, C. jejuni promotes an asymptomatic, intestinal colonization of many animals, especially avian species, to result in commensalism. The primary route of transmission to humans is through the consumption or handling of undercooked poultry meats, making C. jejuni of particular importance to the agricultural industry. The direct interplay between C. jejuni and the natural avian host was examined to better understand the interactions that contribute to commensalism. We analyzed the colonization dynamics of C. jejuni over 28 days and identified a previously uncharacterized prolonged, robust colonization of the bursa of Fabricius, a major lymphoid organ. C. jejuni localized to the mucus layer lining the epithelium of the bursal lumen, with no invasion of or damage to host tissue apparent. However, C. jejuni was detected invading the cecal epithelium of chicks but only at day 1 post-infection, which may contribute to the observed transient, infection of the spleen and liver. Additionally, certain colonization factors of C. jejuni were shown to promote persistence in specific organs. Mutants lacking catalase and the cytolethal distending toxin demonstrated a reduction in levels in the bursa but not the ceca during prolonged colonization, whereas an unencapsulated mutant showed a global colonization defect of all organs. These findings suggest that persistent colonization of the bursa and the ceca, and the ability of the avian host to largely confine C. jejuni to mucosal surfaces may be specific for the development of commensalism. Separate analyses of additional colonization factors of C. jejuni revealed the importance of two putative cytochrome c peroxidases (CCP), DocA and Cjj0382, in promoting efficient cecal colonization. Further analysis of DocA and Cjj0382 revealed that both proteins have typical characteristics of CCPs, as they are periplasmic proteins with heme-dependent peroxidase activity. Our data suggest that although DocA and Cjj0382 have characteristics of CCPs, they likely perform different physiological functions for the bacterium during colonization. Overall, this study enhances our understanding of the interactions between C. jejuni and a natural host that contribute to the development of commensalism.