IAI Accepts, published online ahead of print on 15 September 2008

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Infect. Immun. doi:10.1128/IAI.00786-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of a Bile-Induced Exopolysaccharide Required for Salmonella Biofilm Formation on Gallstone Surfaces

Robert W. Crawford, Deanna L. Gibson, William W. Kay, and John S. Gunn^*

Center for Microbial Interface Biology and Department of Molecular Virology, Immunology, and Medical Genetics, The Ohio State University, Columbus, Ohio 43210; Division of Gastroenterology, University of British Columbia and BC Children's Hospital, Vancouver, British Columbia, Canada; Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada

^* To whom correspondence should be addressed. Email: gunn.43{at}osu.edu.

Salmonella Typhi can establish a chronic, asymptomatic infection of the human gallbladder, suggesting this bacterium utilizes novel mechanisms to mediate enhanced colonization and persistence in a bile-rich environment. Gallstones are one of the most important risk factors for developing carriage, and we have previously demonstrated that salmonellae form biofilms on human gallstones in vitro. Thus we hypothesize that bile-induced biofilms on gallstone surfaces promote gallbladder colonization and maintenance of the carrier state. A colanic acid, cellulose S. Typhimurium double mutant formed a mature biofilm on gallstones in a test tube assay and in a new, gallstone-independent assay using cholesterol-coated Eppendorf tubes. These data suggest the presence of an unidentified exopolysaccharide necessary for mature biofilm development and demonstrate specific binding affinity between Salmonella and cholesterol. Our experiments indicate that Salmonella O-antigen capsule (yihU-yshA/yihV-yihW) is a crucial determinant in gallstone and cholesterol biofilms, whereas expression of this exopolysaccharide is not necessary for binding to glass or plastic. Real-time PCR revealed that growth in bile resulted in upregulation of the O-antigen capsule-encoding operon in an agfD independent manner. Thus, the O-antigen capsule genes are bile-induced and the capsule produced by the enzymes of this operon is specifically required for biofilm formation on cholesterol gallstones. These studies provide new therapeutic targets to prevent asymptomatic S. Typhi gallbladder carriage.

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