The role of commensal organisms as pro-infectious agents in Staphylococcus aureus infection dynamics.

Staphylococcus aureus is an important human pathogen that causes significant death and disease around the world. The problem is exacerbated by the spread of antibiotic resistant strains such as Methicillin Resistant S. aureus (MRSA). MRSA is generally a hospital-associated infection but recently community acquired MRSA has increased in the apparent absence of antibiotic selection. Thus there is a constant need to develop new control regimes for S. aureus, as this organism has begun to show resistance even to new antibiotics such as linezolid and no vaccine is available. To win this battle we must not only produce new treatments and preventative measures but also to understand the complexities of how S. aureus causes disease and thus how interventions can be best utilised, to reduce the disease burden and to minimise the development and spread of resistance to antibiotics. How do humans get infected with S. aureus? We have made the astonishing discovery that relatively harmless skin organisms and even their component cell walls are able to cause significant exacerbation of S. aureus infection, allowing disease to occur with a hugely reduced infectious dose. The most common route of human infection is via a wound and of course this will occur with whatever material gets in, including S. aureus. We have named the material that can augment S. aureus infection as "pro-infectious agents". We have opened a window on natural infection and in doing so provide novel avenues for trying to understand disease and how we may prevent it. The current application takes an interdisciplinary approach to understand how infection is initiated, the nature of material and organisms that can act as pro-infectious agents, how infection progresses and how such knowledge may be utilized to prevent and/or cure disease. Our background work and that proposed necessitates an integrated team led by a microbiologist and a clinician with research expertise in innate immunity. This combined expertise, coupled with important partners around the world, provides a proven network to underpin our ambitious proposal.

Our work is underpinned by the use of animal models of infection, as this complex process cannot be recapitulated in vitro without understanding of what happens in vivo. We have uniquely developed the vertebrate zebrafish embryo as a model of S. aureus systemic disease. This provides a high-throughput, genetically tractable system where host:pathogen interaction can be observed in a living host. The importance of this model is that it has not only provided important insights into pathogenesis but has also informed our use of a mammalian system thus replacing many mouse experiments directly, reducing the numbers of mammals used and refining our approach. We will use a combination of animal models, together with in vitro analysis to determine the breadth of material that can augment S. aureus infection and the cellular and molecular mechanisms underlying this effect. Infection will then be mapped from initiation to endpoint in order to identify bottlenecks as sites for the development on novel intervention strategies. We will use a variety of approaches including state-of-the-art intravital microscopy in all models to determine the pathway of infection.

The application provides an integrated package that will further our understanding of disease mechanisms and how this information may be used to inform clinical practice.

S. aureus is able to cause a wide range of diseases, with no vaccine available and antibiotic resistance common. It is therefore crucial to understand how S. aureus infection is initiated and progresses in order to identify novel clinical interventions. We have made the exciting discovery that skin commensal organisms, and even their isolated cell walls, can augment S. aureus infection. We have called the augmenting material "pro-infectious agents" and have shown its addition to result in a massive decrease in the inoculum of S. aureus required to cause serious disease. These findings are extremely pertinent to human infection, as this will always occur from within a polymicrobial milieu. It is important now to capitalize on our initial results to understand the breadth and basis of the augmentation phenomenon and how this might be exploited in the development of new approaches to tackle S. aureus.
The project will take an interdisciplinary approach, with global partners, using a combination of in vivo and in vitro analyses. We will investigate the molecular basis of pro-infectious agents in terms of those organisms and components able to augment S. aureus disease, coupled with an elucidation of the host response to pro-infectious agents from the molecular, through cellular to the whole host level. This will be set within a determination of the progression of S. aureus infection to understand how disease is established as a complex interaction between host and pathogen and how this dynamic is altered by the presence of pro-infectious agents. Finally, we will examine how our discovery of pro-infectious agents can be utilized in the design of a vaccine and other immunological interventions. Such ambitious goals, from fundamental understanding to translation, can only be achieved via an integrated team of investigators and partners, providing molecular understanding of host:pathogen interaction with important ramifications for human disease.

The proposed project will develop an integrated, interdisciplinary platform to study S. aureus disease and the effect of prophylactic and treatment regimes. There will be a variety of impacts over a range of timescales and arenas.

- Academia (expected timescale year 1 onwards): will benefit from the information gained during the project, communicated both orally and via publication. Also given the unique use of the zebrafish embryo model of S. aureus pathogenesis, Sheffield will become a hub for collaboration and training. Transgenic zebrafish lines generated in this project will have diverse utility for other applications. The innovative multidisciplinary approaches we are taking will be a model for others working on related problems.

- Industry (expected timescale year 2 onwards): will benefit as potential users of the data concerning the use of antibiotics and the establishment of pathogen population dynamics during infection to test existing or develop new control regimes, such as vaccination. Direct links to Biotech companies such as Absynth and pharmaceutical companies such as GSK are in place to facilitate direct translation of key findings.

- National Health Service (expected timescale year 2 onwards): The cost to the NHS of healthcare associated infections (of which MRSA is the most significant) has been estimated by the HPA to be £1billion a year in England alone. This is predominantly in terms of delayed discharge, with associated knock-on effects of full hospitals, cancelled operations and lack of beds for non-emergency admissions. If we were able to identify new ways to treat or prevent MRSA, this would have a major impact on the NHS.

- Government bodies (expected timescale year 2 onwards): will benefit from the information on the role of microflora in disease augmentation as it will inform decisions as to decontamination of wound sites.

- Local communities (expected timescale year 2 onwards): via outreach activities will benefit from greater knowledge of this scientific area and engagement with scientific advances made locally.

- Society more broadly (expected timescale year 2 onwards): will benefit if the findings of this project translate to a reduction in the spread of antibiotic resistant bacteria, or new strategies for the treatment of infectious disease.

- UK PLC (expected timescale year 2 onwards): will benefit through the development of commercial activities, and added value to both biotechnology and pharmaceutical companies. In addition, the economic burden of MRSA infection in the UK can be counted in the billions of pounds, from missed work and additional costs following hospital discharge. Small reductions in spread of antibiotic resistance could have large impacts on the productivity of the UK workforce.

- Undergraduate/postgraduate/post docs (expected timescale year 1 onwards): will benefit through development of skills in cell biology, microscopy, in vivo studies etc. cascaded down through teaching interactions within the lab.

- Media (expected timescale year 1 onwards): will benefit through the applicants' participation in radio and newspapers interviews.