Salmonella and Probiotics
Research objectives
The S&P group pursues the search for effective alternatives in curing and prevention of infectious bacteria-mediated diseases by studying the molecular mechanisms of the interactions involved. Therefore, we focus on two bacterial species, i.e. the intestinal pathogen Salmonella enterica serovar Typhimurium ( S. Typhimurium) and the probiotic strain Lactobacillus rhamnosus GG.
This research was initiated in 2000 by studying the interactions between probiotics , bacterial pathogens and intestinal epithelial cells at the molecular level. To this end, we implemented new technologies for image analysis and differential gene expression at the CMPG. Since then, both hypothesis-generating high-throughput technologies and into-depth molecular analyses are applied to explore the potential of different strategies to secure human and animal health.
Current research: Salmonella
Salmonella systems biology
Salmonella pathogenesis involves the complex interaction of regulatory pathways which play different roles in various stages of infection. Detailed k nowledge on these pathways, taking all intricacies into account, ultimately will lead to the development of alternative and more targeted preventive and curative anti- Salmonella treatments. The ultimate goal is the reconstruction of regulatory networks by generating and integrating heterogeneous data from wet lab experiments, combined with in silico predictions (e.g. motif data). Currently, pathways under study are related to Salmonella invasion, bacterial cell-cell communication and biofilm formation.
Wet lab high-throughput data are generated at different levels:
- Transcriptome data (in-house constructed Salmonella microarrays)
- Proteome data (2D-DIGE platform implemented)
- ChIP -chip data: ChIP -chip combines the selective isolation of all regulator-DNA binding site complexes out of the cell (chromatin immunoprecipitation or ChIP ) with a global identification of target genes by microarray hybridization (chip). Doing so, all direct and in vivo target genes of a regulatory protein can be determined on a genome wide scale.
For this part of the research, we work in close collaboration with the Bioinformatics group of CMPG. We are also a partner of SymBioSys, the K.U.Leuven Center for Computational Systems Biology, an interfaculty platform that brings together top expertise in bioinformatics, statistics, and life sciences from 7 K.U.Leuven partners.
Salmonella quorum sensing interference
A major problem in the treatment of Salmonella infections is the increasing number of Salmonella strains that are resistant to multiple antibiotics. Several bacterial pathogens use cell-cell communication systems, also known as quorum sensing (QS) systems, to regulate the expression of virulence factors. This part of our research focuses on the chemical synthesis of mimics of QS signals (in collaboration with Prof. D. De Vos , COK) and the study of their biological activity on the QS systems of Salmonella Typhimurium. We are interested in the identification of molecules that are able to activate or inhibit these QS systems as well as compounds that inhibit the biofilm formation by S. Typhimurium. Such compounds might be used as alternatives for antibiotics.
Current research: Probiotics
Characterization of genes involved in colonization and immunomodulation of L. rhamnosus GG
Although Lactobacillus rhamnosus GG, a human isolate, is one of the clinically best studied probiotic strains, the basic molecular mechanisms of its beneficial actions are mainly unknown. Moreover, the understanding of the physiology and genetics of this bacterium is still limited. Therefore, we optimized different genetic tools, that enable us to study mechanism of action at the gene level. Hereto, we focus on genes involved in cell-wall properties, adherence, colonization, immunomodulation and bacterial cell-cell communication by construction of specific knock-out mutants and their phenotypic analysis. Additionally, ' in vivo expression technology' (IVET) is applied to investigate genes necessary for persistence of L. rhamnosus GG in the gut.
Molecular mechanisms of bacteria-host interactions in the gut: inflammatory bowel diseases as a case study
The interest in the role of commensal bacteria in human health is increasing drastically since the 'hygiene hypothesis' links reduced exposure to beneficial gut bacteria (related to modern living conditions) with a rising incidence of human allergies, auto-immune diseases and inflammatory bowel diseases (IBD). In this part of the research, we aim to analyze mechanisms of probiotic-host interactions in relation to inflammatory bowel diseases. Hereto, two model probiotic organisms are studied, i.e. Lactobacillus rhamnosus GG and Bifidobacterium lactis Bb12. Mechanisms of probiotic action are investigated by an integrated approach including microbial genetics, in vitro assays for probiotic characteristics, studies in an animal model for IBD and a clinical study in IBD patients. Biofilm formation of commensal and probiotic bacteria is studied in vitro and in vivo by application of fluorescence in situ hybridization (FISH). Moreover, the role of surface polysaccharides in immunomodulation is studied in vitro with intestinal epithelial cell lines and in vivo in relation to DSS-induced colitis in mice. This part of the research is performed in collaboration with Prof. P. Rutgeerts , Prof. J. Ceuppens and Prof. K. Geboes.
Characteristics of probiotics related to prebiotic consumption
Prebiotics are defined as "non digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon". Unfortunately, the main mechanisms whereby prebiotics exert protective or therapeutic effects are not fully elucidated. In this project the role of prebiotic compounds in the metabolism, adherence to human intestinal epithelium and gene expression of probiotic strains, including L. rhamnosus GG, will be determined. This project is a collaboration with Prof. J. Delcour (IMPAXOS).
