Interaction of Staphylococcus aureus and humans: Iron regulated surface proteins and a novel host defence mechanism

Lead Research Organisation: University of Sheffield
Department Name: Molecular Biology and Biotechnology

Abstract

Staphylococcus aureus is an important human pathogen, particularly in hospitals where it kills many people each year. The problem is compounded by the spread of antibiotic resistance and we know the organism best as MRSA (methiciliin resistant S. aureus). We have identified a number of S. aureus components that are being developed as a vaccine to prevent disease and spread of the bug. We have also found that one of these bug proteins protects it against a number of the mechanisms we humans make to defend ourselves. In doing so we have found a new way in which humans are able to turn off the toxins made by S. aureus. We will find out how this mechanism works and how the bug is able to defend itself in this battle. The research will define how the bugs and we have evolved to interact with each other and give novel potential avenues to sway the outcome in our favour.

Technical Summary

Staphylococcus aureus is a major human pathogen of increasing importance due to the spread of antibiotic resistance. It is relatively ubiquitous in the human environment due to nasal carriage. At present there is no vaccine available. As part of a large study we have identified S. aureus antigens expressed during human infection. In particular we have found an iron regulated surface protein (IsdA), required for nasal colonisation. Vaccination against IsdA protects against nasal carriage and it (alongside other proteins) is currently being developed as a potential human vaccine. IsdA is an adhesin, required for binding S. aureus to human nasal squamous cells. IsdA also makes S. aureus more hydrophilic and is involved in resistance to human innate defence mechanisms, including defensins and skin fatty acids. Our analysis has identified a novel innate defence mechanism whereby human skin fatty acid is able to inhibit virulence determinant production and IsdA is required for resistance to this. IsdA is a member of a 4-protein family, the others with ill-defined roles.

The aims of the project are to characterise the roles of the 4 wall-associated Isd proteins of S. aureus, in particular IsdA, in host:pathogen interaction, cellular physiology and the action of antibiotics. Also the molecular basis and extent of the novel innate defence properties of skin fatty acids will be determined. The research objectives will determine the roles of the Isd proteins by creation of single and multiple mutants and the heterologous expression of proteins. The genetic constructs will be used to define ligand-binding capacity, resistance to host defences, role in iron acquisition and interaction with animal and human hosts. How IsdA is able to carry out its various functions in host defence resistance will be analysed by expression of individual domains (and sub-domains) and functional analysis. The mechanism of action of human fatty acids on bacterial survival and virulence determinant production will be determined using a combination of physiological, biochemical and genetic approaches. Finally the involvement of skin fatty acids and IsdA in the sensitivity of S. aureus to antibiotics will be elucidated. The ability of fatty acids to potentiate the activity of specific antibiotics will also be tested.

The project will define a novel mode of human innate defence, which might be important against a wider range of pathogens. Also the role of bacterial components in host resistance will be elucidated, as important facets of host:pathogen interaction.

Publications

10 25 50

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ValegÄrd K (2013) Structural and mechanistic studies of the orf12 gene product from the clavulanic acid biosynthesis pathway. in Acta crystallographica. Section D, Biological crystallography

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Neumann Y (2015) The effect of skin fatty acids on Staphylococcus aureus. in Archives of microbiology

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Batson S (2010) Crystallization and preliminary X-ray analysis of a D-alanyl-D-alanine ligase (EcDdlB) from Escherichia coli. in Acta crystallographica. Section F, Structural biology and crystallization communications

 
Title Bacterial Strains 
Description Several defined bacterial strains have been produced 
Type Of Material Biological samples 
Year Produced 2007 
Provided To Others? Yes  
Impact No subsequent impact 
 
Title Human Skin fatty acid 
Description Purified skin fatty acid 
Type Of Material Technology assay or reagent 
Year Produced 2009 
Provided To Others? Yes  
Impact No subsequent impact 
 
Description Antibiotic Resistance 
Organisation Uppsala University
Country Sweden 
Sector Academic/University 
PI Contribution We study S. aureus interaction with the host using animal models
Collaborator Contribution Swapping of prepublication results and protocols
Impact A funded EU grant. This is multidisciplinary research spanning clinical samples, microbiology, modelling etc.
Start Year 2010
 
Description School Visit 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Primary Audience Schools
Results and Impact Visit by secondary school children. Demonstration of practical microbiological research

No subsequent impact
Year(s) Of Engagement Activity 2007
 
Description School visits 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Introduction to microbiology and the interaction of microbes with the human host. A mixture of presentation and practical

No subsequent impact
Year(s) Of Engagement Activity 2009,2010,2011,2012,2013