Compound Profiling und Screening
New strategies for new active agents against infections from commensal and persistent bacteria
Bacteria cause infections when they can spread and proliferate unrestrained in the body and the organs of a colonized host. Thus, infections usually result from a pathogen’s penetration of protecting barriers such as skin, mucosa or blood vessels, dissemination via the bloodstream, escape from the immune system and adaptation to the physical and chemical conditions of the newly colonized body niche. Existing antibiotics control spread of bacteria by targeting structures and reaction pathways which are essential for growth and proliferation under almost all conditions, such as protein synthesis or biosynthesis of cell wall components. Consequently, these agents can be widely used, but also resistances rapidly develop and spread. However, it is increasingly recognized that bacteria adapt to their environmental conditions by adjusted gene expression, protein activities and metabolic pathways. Thus, growth and proliferation of a pathogen in a specific body niche may require not only the general essential structures and pathways mentioned above, but also additional proteins, which are essential in only a limited number of body niches and thus could also be exploited as targets for drugs. The application of such drugs would be limited to the treatment of infections of the respective or related body niches. This would contribute to a reduced rate of development and spread of resistant strains, as the applied amounts of such drugs are lower and the selective pressure is also limited to bacteria in the respective body niche.
Profiling of Chemical Compounds
We characterize (new) chemical compounds with respect to biological activities to continuously expand the accessible and exploited chemical space. Thus, we routinely perform antibacterial assays under laboratory conditions, and also evaluate the cytotoxic potential of compounds in cell-culture assays. Gram-negative bacteria are inherently more resistant to antibiotics, due to the low permeability of the outer membrane of the cell wall and the high efficiency of drug efflux pumps. Thus, we also use mutant strains, which show increased compound uptake characteristics, to roughly evaluate potential resistance mechanisms. Secondary assays can be performed which show an influence on membrane integrity, membrane potential, respiration and also on the metabolomic and transcriptomic profile of the bacteria (cooperation within the HZI).
Inhibition of Virulence Mechanisms
We aim at the inhibition of mechanisms which allow the pathogen to break the protecting functions of the host and to survive, proliferate and spread in the host and thus successfully establish an infection. We have chosen Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa as target organisms, which are bacteria classified as priority bacteria by the WHO due to their broad resistance profiles, and which cause infections of different organs in the body.
We establish assays and assay systems, which target these virulence mechanisms and which allow screening for new active compounds. These are mainly phenotypic, miniaturized cellular assays, eventually based on bacteria and representative host cells, to be as close as possible to the real conditions during infection. But we can also use protein-based assays. Our compound sources are natural products from our colleagues, but also compounds from chemical synthesis so that we can perform pilot screens with up to 30.000 to 35.000 compounds. For further evaluation of active compounds we also perform more complex analysis in secondary assays, such as metabolomics studies in cellular host – pathogen – infection models.
Breaking Resistance Mechanisms
Some resistances against antibiotics are either generated or acquired over time and are based on modifications of the target, so that the antibiotic is not active anymore. Other bacteria are inherently resistant against some classes of antibiotics, as they possess enzymes, which chemically modify and inactivate the chemical compound (β-lactamases inactivate β-lactam antibiotics) or restrict the access of the antibiotic to its pathogen. The latter is an important resistance mechanism of Gram-negative bacteria, as the asymmetric outer membrane and effective drug export pumps lead to low, sub-antibiotic intracellular concentrations of the drugs. We screen for compounds, which inactivate or bypass these mechanisms so that the intracellular drug concentrations increase and Gram-negative bacteria are sensitized for such drugs.
Bachelor & Master
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