Knowledge for Growth location:Ghent date:7 May 2009
A major difficulty in the control of Salmonella enterica infections is the fact that Salmonella can form multicellular structures, commonly called biofilms, on various biotic and abiotic surfaces. Within these biofilms, Salmonella is much less sensitive to disinfectants, antimicrobial treatment and the immune system of the host. Given the importance of biofilm formation in the spread and persistence of Salmonella, our research aims at the elucidation of the genetic factors determining biofilm formation and at the development of effective anti-biofilm treatments. One of the technologies used to identify Salmonella genes involved in biofilm formation is the Differential Fluorescence Induction (DFI) strategy which allows selecting important genes at a single-cell-based level. This is an advantage since a biofilm consists of a heterogeneous bacterial population. DFI is an enrichment strategy which uses a library of small fragments of genomic DNA (S. Typhimurium genomic DNA), cloned upstream of a promoterless gfp-gene and a fluorescence-activated cell sorter (FACS) to monitor promoter activity under specific environmental conditions (biofilm formation). As a complementary strategy we are screening a S. Typhimurium mutant library under biofilm conditions to search for mutants with altered biofilm behavior. Interesting genes resulting from these genome-wide searches will be functionally characterized to elucidate important biofilm related gene regulatory networks. This knowledge can be used for the development of effective anti-biofilm treatments, which is based on two approaches. In the bottom-up approach we search for inhibitors of specific cellullar targets that play a key role in biofilm formation, by using receptor based computational approaches or by screening of compound libraries using reporter fusions of target genes involved in biofilm formation. In the top-down approach we perform screenings of libraries of chemical compounds and natural product analogues to identify molecules that are able to prevent Salmonella biofilm formation or to disperse mature biofilms. We have already discovered different classes of Salmonella biofilm inhibitors of which we are currently studying the exact mode of action by using a variety of techniques such as gene reporter fusions, transcriptome and proteome analyses and screening of a mutant library for mutants that are hypo- or hypersensitive to the biofilm inhibitors. To optimize the structure of the biofilm inhibitors we will use ligand based computational techniques, such as 3D-QSAR. The combination of our fundamental and applied approach will eventually lead to the development of effective anti-Salmonella treatments, urgently needed to comply with the new EU directives to reduce the number of zoonotic infections.