Characterization of Bacterial and Host Factors During Early Campylobacter jejuni Colonization Events in the Chicken Gastrointestinal Tract.

Abstract

Campylobacter jejuni is a leading cause of bacterial gastroenteritis in the United States and is primarily acquired through ingestion of contaminated poultry products. C. jejuni colonizes the gastrointestinal tract of chickens asymptomatically, with the primary site of robust bacterial colonization being the mucus layer deep within the crypts of the cecum. The research presented in this thesis focuses on identifying and characterizing factors and events critical in the establishment of a C. jejuni persistent colonization in the chick cecum. We show that upon inoculation, C. jejuni invades the epithelial layer and stimulates a modest inflammatory response characterized by expression of pro-inflammatory cytokines and influx of avian polymorphonuclear cells (termed heterophils) in the cecum. We demonstrate that local invasion is dependent on C. jejuni virB11, a gene encoding a putative type IV secretion system ATPase that is not required for colonization. Inflammation evenutally subsides and C. jejuni persists in the cecal contents without evident symptoms of pathogenicity. However, C. jejuni is recovered from systemic sites (such as the spleen and liver), and antibodies are produced against C. jejuni antigens. Efforts to determine bacterial factors required for benign colonization of the chicken intestinal tract led to identification of a high affinity zinc ABC transporter in C. jejuni and characterization of ZnuA, a zinc-binding periplasmic glycoprotein that is modified by the N-glycosylation system and is essential for chick cecal colonization. Zinc is an essential trace element and many bacterial species encode high affinity zinc ABC transporters (ZnuABC) to acquire zinc in limiting environments. Evaluation of the mechanisms that limit the colonization potential of zinc uptake mutants led to the finding that zinc is limiting in the cecum due to the presence of the microbiota; without znuA, C. jejuni is unable to acquire zinc necessary for replication. A C. jejuni mutant lacking znuA colonized chicks with a limited-flora, but competed unsuccessfully in the presence of conventional cecal microbiota. We hypothesize that the microbiota use and store zinc, as well as modify host metabolic processes, thereby lowering the amount of avialbale zinc in the chick ceca.