Salmonella binding to and biofilm formation on cholesterol/gallstone surfaces in the chronic carrier state

The Gram-negative pathogen Salmonella enterica serovar Typhi is the etiologic agent of human typhoid fever, a systemic illness characterized by high fever, bradycardia, and muscle pain. A percentage of these infections can result in asymptomatic carriage of salmonellae in the bile-rich gallbladder, and we have previously demonstrated that salmonellae can form biofilms on the surface of human cholesterol gallstones as a mechanism that contributes to the development of the carrier state. To determine which genes/ligands mediate the ability of Salmonella to bind and form biofilms on cholesterol, mutants of S. enterica serovar Typhimurium were created through random transposon mutagenesis. These mutants were screened for impaired biofilm formation on cholesterol-coated Eppendorf tubes in the Tube Biofilm Assay (TBA) but normal biofilm formation on glass and plastic surfaces. Of the 49 mutants with this phenotype, 70% of the disrupted genes were involved in flagella or fimbriae biosynthesis. Independent assays demonstrated that the presence of flagella were important for adherence to cholesterol and biofilm initiation, while over-expression of fimbriae was inhibitory. The remaining transposon insertions, located in sseI and ompC, had no effect on cellular motility, suggesting a mechanism of action independent of flagellar-mediated adherence to cholesterol. Subsequent analysis of sseI and related mutations in the TBA suggested that SPI-2 genes are important for the formation of biofilms in the presence of bile, but unimportant for biofilm formation in the absence of bile. Similar analysis of ompC in the TBA demonstrated that the observed loss of biofilm formation was not due to changes in the osmolarity of the extracellular environment. These studies provide a better understanding of how salmonellae form biofilms in the presence of bile and suggest a target for therapies that may alleviate biofilm formation on cholesterol gallstones and the chronic carrier state.National Institutes of HealthOSU Public Health Preparedness for Infectious DiseasesNo embarg