Exploitation of quorum sensing for the discovery of novel agents against staphylococci

Lead Research Organisation: University of Nottingham
Department Name: Sch of Molecular Sciences

Abstract

The emergence, rapid spread and persistence of multi-antibiotic resistant bacteria constitutes a global health threat. The World Health Organization has stated that ?no population is more vulnerable to multi-antibiotic resistance than those admitted to hospital wards?. In the UK, healthcare associated infections account for over 5000 deaths annually and are associated with enormous personal and financial costs to the individual, their family and to the NHS (estimated at over #1 billion p.a.). In this context, both hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) and Clostridium difficile are particularly problematic. This is not only a consequence of their ability to cause disease but also because antibiotic usage increases resistance and infection rates. Recently new ?community acquired? MRSA strains (CA-MRSA) have emerged which cause invasive infections in healthy young people. Against this backdrop, the development of new classes of antibiotics has lagged far behind the urgent requirement for new drugs, in part because of the reluctance of major pharmaceutical companies to develop expensive new drugs likely to become rapidly obsolete through resistance. Consequently we need to gain better insights into the infection-specific lifestyle of bacteria if we are to discover new ways of preventing and treating infection and reducing the selection of resistant strains. In this project we are seeking to understand how MRSA bacteria use chemical signals to communicate with each to make decisions about when to deploy the armoury of toxins they need to fight off human host defences, grow inside human cells and damage tissues. By understanding the chemical nature of these signals, the way in which they are produced by the bacterial cell and sensed by receptor proteins on the bacterial cell surface we will develop new drug molecules capable of controlling infection by blocking this signalling system. So far we have discovered three different families of small molecules which either inhibit signalling or growth or both. We will therefore use medicinal chemistry and biological approaches to understand how these compounds work at the molecular level and use this information to design agents with increased potency in antibacterial assays in the laboratory. The most promising compounds will be tested for efficacy in experimental animal infection models. The work with focus on primarily MRSA but promising compounds will also be tested against C. difficile and related pathogens.

Technical Summary

Staphylococcal infections are of major clinical importance. MRSA strains which exhibit multi-antibiotic resistance and cause invasive infections in healthy individuals constitute a serious health threat. While resistance has evolved against virtually every antibiotic deployed, the development of new classes of antibiotics has lagged far behind the urgent requirement for new drugs. Many major pharmaceutical companies have withdrawn from the antibiotic discovery field mainly because of the huge economic cost of developing drugs likely to become rapidly obsolete through resistance. Thus, there is an urgent need to identify novel antibacterial targets and develop new agents effective against multi-resistant bacteria. This in turn depends on a thorough understanding of the basic molecular biology and physiology of bacterial pathogens. In this context, the attenuation of virulence through the blockade of sophisticated global regulatory systems such as quorum sensing (QS) offers an attractive target. In S. aureus, the agr QS system, which is also shared by Gram positive pathogens including Listeria, Enterococcus and Clostridium, is central to virulence gene regulation, intracellular survival and biofilm development and dispersal. Here we propose to build on our previous work by employing a multidisciplinary research strategy combining chemical biology with bacterial physiology and in vivo studies to obtain detailed molecular insights into (a) the recognition of auto-inducing peptide (AIP) signal molecules by the histidine sensor kinase receptor, AgrC, and (b) the generation and export of AIPs via the transmembrane enzyme, AgrB. Unexpectedly, both growth and agr-dependent QS in S. aureus can be inhibited by Gram negative bacterial QS signal molecules and we have discovered analogues (tetramic and tetronic acids) which exhibit potent activity against staphylococci and other Gram positive bacteria including Clostridium difficile. In addition we have identified a class of thiol-reactive aryl quinones which inhibit agr potentially through the inactivation of SarA family proteins in S. aureus which regulate virulence via agr-dependent and -independent mechanisms. We will therefore undertake extensive structure activity relationship, mechanistic and translational studies on the each compound class to elucidate their mechanisms of action and to develop agents with increased potency. The most promising compounds including novel AIP antagonists will be investigated for their activity against planktonic, biofilm and intracellular staphylococci in laboratory culture and for in vivo efficacy in experimental animal infection models. The work has broad implications for antibacterial agent discovery beyond S. aureus given the conservation of agr systems in Gram positive pathogens and two component systems in bacteria generally

Publications

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Harraghy N (2005) sae is essential for expression of the staphylococcal adhesins Eap and Emp. in Microbiology (Reading, England)

 
Description MRC Programme Grant
Amount £1,690,000 (GBP)
Funding ID G9219778 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 07/2009 
End 06/2014
 
Title Bacterial Intracellular Growth Assay 
Description We developed an in vitro high throughput cell culture-based method to investigate the intracellular behaviour of bacteria such as the staphylococci and for screening the intracellular efficacy of antimicrobial agents 
Type Of Material Technology assay or reagent 
Provided To Others? No  
Impact Joint publications with other EU research groups 
 
Title Quorum Sensing Inhibitors 
Description A chemical library of compounds has been synthesized and screened for the ability to inhibit staphylococcal virulence through the inhibition of quorum sensing 
Type Of Material Technology assay or reagent 
Provided To Others? No  
Impact Publications - see section 2 
 
Description Agr-dependent quorum sensing and methicillin resistance 
Organisation University of Bath
Department Department of Biology and Biochemistry
Country United Kingdom 
Sector Academic/University 
PI Contribution Intellectual contribution, experimental design and synthesis of quorum sensing signal molecules
Collaborator Contribution Joint experimental work leading to a publication
Impact Publication in press in Journal of Infectious Diseases (2010)
Start Year 2010
 
Description Eap and Emp proteins 
Organisation Saarland University
Department Institute of Medical Microbiology and Hygiene
Country Germany 
Sector Academic/University 
PI Contribution application of the intracellular staphylococcal assay to evalute contribution of Eap and Emp proteins to growth
Collaborator Contribution Collaborative experiments on the role and regulation of the staphylococcal cell wall proteins Eap and Emp
Impact Joint Publication - see section 2
 
Description Intracellular assays and Clp proteases 
Organisation University of Copenhagen
Department Royal Veterinary and Agricultural University
Country Denmark 
Sector Academic/University 
PI Contribution Application of intracellular replication assays to the role of staphylococcal clp proteases
Collaborator Contribution Collaboration on the role of Clp ATPases in stress tolerance, intracellular replication and biofilm formation in Staphylococcus aureus
Impact Joint Publication - see section 2
 
Description Mathematical Modelling of Quorum Sensing 
Organisation University of Nottingham
Department School of Mathematical Sciences Nottingham
Country United Kingdom 
Sector Academic/University 
PI Contribution Input of biological knowledgene into the development of mathematical models
Collaborator Contribution Development of mathematical models of bacterial virulence gene regulation
Impact Publications - see section 2
Start Year 2006
 
Description BBC1 Programme 'Bang goes the Theory' 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Paul Williams gave an interview in his Nottingham laboratory on quorum sensing and novel antibiotics filmed for Series 3 Episode 4 of 'Bang goes the Theory'. Specific Viewing figures for the episode broadcast on 4 April 2011 not known but audiences of 2-3 million per episode have been reported.

None identified as yet
Year(s) Of Engagement Activity 2011
 
Description Electronic Encyclopedia Article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact On-line article on quorum sensing for the Encyclopaedia of Life Sciences. See:(http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0001426/current/html?hd%3DAll%2Cquorum)

Not known
Year(s) Of Engagement Activity 2007
 
Description Media Briefing - Science Media Centre 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Primary Audience Media (as a channel to the public)
Results and Impact Press interview given on antibiotics and antibiotic resistance at the Science Media Centre in London to newspaper science journalists

None known
Year(s) Of Engagement Activity 2007
 
Description Nottingham Welsh Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation Keynote/Invited Speaker
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact About 30 people attended the presentation on 'plagues - ancient and modern in which I talked about antibiotic resistance MRSA and C.difficile. The talk was followed by a lively Q&A session

None known
Year(s) Of Engagement Activity 2012
 
Description Public Art and Science Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact A presentation on microbes and quorum sensing at a public workshop entitled 'Discovering the invisible - photography in art and science at the Lakeside Theatre Nottingham (30th June 2007).

Not known
Year(s) Of Engagement Activity 2007
 
Description Quorum Sensing Web Site 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact We have established a web site (www.nottingham.ac.uk/quorum) which explains the basics of bacterial cell-cell communication for both public and specialist audiences, It also acts as a one stop shop linking all those working or interested in the field.

The site has received 73943 hits since September 2006 and has been approved by the Thomson Thompson ISI Current Web site for its authority, accuracy, currency, navigation and design and quality of writing
Year(s) Of Engagement Activity 2006,2007,2008,2009
 
Description Radio 4 Programme 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Contributions made to a 2 part BBC Radio 4 programme on the "Rise of Resistance" Part 1 and 2 with Dr Mark Porter (brodacast on 04/07/07 and 11/04/07)

Not known
Year(s) Of Engagement Activity 2007
 
Description University Access 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Primary Audience Schools
Results and Impact Over the last 3 years (Feb 2007, 2008 and 2009) contributions to have been made to the "Get on 4 Uni Masterclasses "which give Year 12 students the opportunity to develop interdisciplinary approaches to learning and to explore, in depth, subjects that they may be interested in studying at university.

Not known
Year(s) Of Engagement Activity 2007,2008