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.
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.
Prof Dr Ursula Bilitewskii
In order to develop therapies for fighting infections caused by new pathogens or resistant microorganisms not only we need new drugs but, more importantly, we need to identify new targets for these drugs to act on.
Ursula Bilitewski studied chemistry at the University of Münster, earning her Ph.D. at the Institute of Physical Chemistry. After spending another year at Münster as a post-doc, she moved to Braunschweig in 1988, where she became part of the HZI – which at that time was called the GBF.
In 1994, she habilitated in biochemistry at the Technische Universität Braunschweig and, since 2002, is an adjunct professor for biochemistry. Her initial research focus, which was on establishing microscale bioanalytical systems, has since shifted to drug research. Her work concentrates on molecular mechanisms and on identifying potential drug targets.
Since 2016, Bilitewski is head of the „Compound Profiling und Screening (COPS)“ research group.
Team
Selected Publications
Günther A., Bilitewski U., (1995) Characterisation of inhibitors of acetylcholinesterase by an automated amperometric flow injection system, Anal Chim Acta, 300: 117-125
Mersal GAM, Khodari M, Bilitewski U (2004) Optimisation of the composition of a screen-printed acrylate polymer enzyme layer with respect to an improved selectivityand stability of enzyme electrodes Biosens Bioelectron 20: 305 - 314
Behnsen* J, Narang* P, Hasenberg M, Gunzer F, Bilitewski U, Klippel N, Rohde M, Brock M, Brakhage AA, Gunzer M (2007) The environmental dimensionality controls the interaction of phagocytes with the pathogenic fungi Aspergillus fumigatus and Candida albicans, PLOS Pathog 3: e13
Bilitewski U,* Blodgett JAV, Duhme-Klair AK, Dallavalle S, Laschat S, Routledge A, Schobert R (2017) Chemical and Biological Aspects of Nutritional Immunity – Perspectives for New Anti-infectives Targeting Iron Uptake Systems Angew Chem Int Ed Engl 56: 14360 - 14382
Publications
Projects
Virulence factor alpha-Hemolysin from Staphylococcus aureus
α-Hemolysin is a pore-forming toxin of Staphylococcus aureus. It targets in particular cells of the human immune system, but also human epithelial and endothelial cells. Thus, it not only damages the immune system but also permeates cell barriers, and its activity enables S. aureus to invade deeper tissues and enter the blood stream so that the pathogen is disseminated in the body. In cooperation with the Lead Discovery Center (LDC), Dortmund we screened for inhibitors of the function of this protein. We now establish cellular host – pathogen systems, which are based on representative host cells (human epithelial cells and human macrophages) and different S. aureus strains and analyse the response of the host to the pathogen and to α-hemolysin. In addition, we study the parameters favoring the production of α-hemolysin beyond high bacterial cell densities (quorum sensing), as this virulence factor is of varying relevance considering different infection sites.
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