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Genetic and molecular basis of methicillin and glycopeptide resistance in Staphylococcus aureus

English title Genetic and molecular basis of methicillin and glycopeptide resistance in Staphylococcus aureus
Applicant Berger-Bächi Brigitte
Number 117707
Funding scheme Project funding (Div. I-III)
Research institution Institut für Medizinische Mikrobiologie Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Medical Microbiology
Start/End 01.11.2007 - 31.10.2010
Approved amount 337'462.00
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Keywords (6)

Staphylococcus aureus; methicillin resistance; glycopeptide resistance; regulation; virulence; fitness

Lay Summary (English)

Lead
Lay summary
The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) is still increasing worldwide. Initially mainly a nosocomial problem, MRSA are now also emerging in the community. Nosocomial MRSA, in an environment of high antibiotic use, rapidly acquire multiresistance, leading to strains that are resistant to all commonly used antibiotics and difficult to treat. Community MRSA in contrast, competing in an environment largely devoid of antibiotica with selection for ecological fitness, are often of very low methicillin resistance and infect healthy persons with no obvious risk factors, suggesting that they are of higher virulence. Although the contribution of methicillin resistance to the severity of infection is still debated, methicillin resistance adds to the virulence of S. aureus both the burden of resistance and an increased potential to develop multiresistance. Pairing extremely virulent community MRSA with the potential to develop high-level resistance to methicillin and acquiring multiresistance to additional antibiotics is a threat that should not be neglected.Genetic evidence suggests that multiple ways may lead to high methicillin resistance in MRSA. The mechanisms(s) conferring high level methicillin resistance, and their functions are not yet clear; nor is it known, if high level resistant MRSA differ in virulence to their isogenic less resistant counterparts. We hypothesize that rapid growth is not compatible with high levels of methicillin resistance, and that a reduced growth rate is consequently the price of high level resistance. Changes in growth rate affect overall metabolism, which in turn has an effect on the expression of virulence factors. If formation of high-level resistance could be prevented, better antibiotic options may again be available against multiresistant MRSA.We are going to identify and characterize the different mechanisms and factors encoded by the staphylococcal genome that contribute to, and modulate resistance to cell wall directed antibiotics. We will measure to which extent they influence staphylococcal metabolism, alter staphylococcal envelope properties, expression of virulence genes and fitness, and will establish a correlation between regulation of resistance and virulence. This involves the analysis of mecA regulation, effects of changes in resistance on global regulators, identification of the induction cascade of the cell wall stimulon; identification and functional analysis of novel factors involved in membrane-associated steps of cell wall synthesis; and of membrane proteins of yet unknown function, shown to influence resistance and virulence.We will characterize a novel chromosomal regulatory element we recently identified, "BlaX", which interferes with transcription of mecA; search for factors involved in the induction pathway of the cell wall stress stimulon; identify and analyze regulatory elements that are under the control of the carbon catabolite repression protein CcpA and characterize the genes controlled by them; functionally characterize a novel membrane protein belonging to the RND efflux pump family and postulated to play a role in the last steps of cell wall synthesis. We will evaluate the fitness of high versus low level resistant MRSA by determining differences in their global transcriptome, and changes in the expression of virulence factors and surface characteristics. In collaboration we will compare the host response to, and the survival, of high versus low level resistant MRSA in animal models.For these purposes we will use state of the art genetic and molecular biological methods, such as random transposon libraries to identify novel factors affecting resistance and surface properties of S. aureus, and develop suitable promoter reporter gene fusions as indicators. We are going to use the bacterial two hybrid system to find interacting partners of membrane proteins thought to be involved in the last step of cell wall synthesis. The extent of regulons controlled by regulatory elements, which we have shown to control resistance and virulence factors, will be identifyed by differential transcriptome microarray analysis. To assess the impact of methiciliin resistance levels and of the genetic background of the stains on fitness and survival, we will use a murine sepsis model in collaboration with R. Landmann, CH , and a Caenorhabditis elegans model in collaboration with C. Sifri, USA.A profound knowledge of the regulatory circuits, of the relevant structural genes, and their functions and interrelation, will assist in the devising of new strategies to combat multiresistance in S. aureus. New potential antibacterial targets may be identified to control and attenuate staphylococcal virulence and fitness. This project contributes in a broad sense to improving the quality of life of patients, to reducing hospital stay and costs, and to the general health of the community.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
105390 Molecular and genetic basis of methicillin resistance in Staphylococcus aureus 01.11.2004 Project funding (Div. I-III)

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