Campylobacter jejuni Cocultured with Epithelial Cells Reduces Surface Capsular Polysaccharide Expression

The host cell environment can alter bacterial pathogenicity. We employed a combination of cellular and molecular techniques to study the expression of Campylobacter jejuni polysaccharides cocultured with HCT-8 epithelial cells. After two passages, the amount of membrane-bound high-molecular-weight polysaccharide was considerably reduced. Microarray profiling confirmed significant downregulation of capsular polysaccharide (CPS) locus genes. Experiments using conditioned media showed that sugar depletion occurred only when the bacterial and epithelial cells were cocultured. CPS depletion occurred when C. jejuni organisms were exposed to conditioned media from a different C. jejuni strain but not when exposed to conditioned media from other bacterial species. Proteinase K or heat treatment of conditioned media under coculture conditions abrogated the effect on the sugars, as did formaldehyde fixation and cycloheximide treatment of host cells or chloramphenicol treatment of the bacteria. However, sugar depletion was not affected in flagellar export (fliQ) and quorum-sensing (luxS) gene mutants. Passaged C. jejuni showed reduced invasiveness and increased serum sensitivity in vitro. C. jejuni alters its surface polysaccharides when cocultured with epithelial cells, suggesting the existence of a cross talk mechanism that modulates CPS expression during infection.The importance of the host cell environment in bacterial pathogenicity is an emerging paradigm in the study of bacterial infection. For example, human colonization creates a hyperinfectious state in Vibrio cholerae that appears to contribute to the epidemic spread of this intestinal pathogen (29). Earlier work with Campylobacter jejuni demonstrated that coculture conditions altered the protein synthesis and virulence of this organism (23). Stintzi et al. demonstrated major effects in gene expression among C. jejuni organisms exposed to pathogenic conditions (36). However, how the host cell environment alters Campylobacter pathogenesis remains largely unknown. C. jejuni is now known to produce capsular polysaccharide (CPS) (4, 21, 31). Although relatively little is known about the contribution of CPS to the pathogenicity of the organism during bacterial interaction with mucosal surfaces, existing data suggest that CPS in general plays a complex and dynamic role in the infection process (2, 33).In a study that was carried out before CPS was identified in C. jejuni, Babakhani and Joens reported that C. jejuni cocultured with primary swine intestinal cells showed increased mucoidy when regrown on solid medium (1). In addition, passaged C. jejuni showed enhanced invasiveness in vitro. We hypothesized that the change in mucoidy observed in these experiments reflected altered CPS expression by bacteria exposed to pathogenic conditions in vitro. We further speculated that altered CPS under these conditions might have relevance to pathogenic behavior among these organisms during infection. In this study, we show that coculture of C. jejuni with human intestinal epithelial cells causes a reproducible reduction in CPS staining. The presence of viable host cells and active protein synthesis by both bacteria and host cells is necessary for the effect on CPS. The alteration in CPS appears to be dependent on a soluble factor that is both heat labile and proteinase K sensitive. Following serial passage with HCT-8 cells, C. jejuni also showed other phenotypic changes, including reduced internalization into HCT8 epithelial cells and increased serum sensitivity.