The horizontal transfer of vancomycin resistance genes from enterococci to Staphylococcus aureus would be a human medical catastrophe, as we are dependent on this antibiotic to treat hundreds of thousands of human S. aureus (including MRSA) infections in the UK every year. For this reason, avoparcin, a glycopeptide antibiotic related to vancomycin, was banned in the EU. This decision was based on the assumption that horizontal transfer of glycopeptide resistance would be accelerated by the use of this antibiotic. These new super-resistant S. aureus would then spread to humans and to hospitals. However, there are several confounding issues with this hypothesis. First, S. aureus, unlike most bacteria, actively blocks uptake of foreign genes from other bacteria. Secondly, animal strains of S. aureus are thought to be quite different to human strains, and it is unlikley that they will colonise, and therefore infect, humans in the same way that human strains do. Thirdly, we do not know if resistance can easily be spread from animal S. aureus to human S. aureus strains. This project will address these issues, providing baseline information that can be used to assess the true risks of antibiotic resistance spreading to clinical S. aureus, and to identify the "red-flag" strains indicating resistance is spreading.