Molecular genetics and evolution of antibiotic resistant staphylococci

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Potentially life-threatening infections caused by Staphylococcus aureus bacteria, commonly known as Golden Staph, often arise as complications in patients within hospitals. These infections compromise the health of the patient and jeopardise their recovery from the condition for which they were initially admitted, which significantly increases healthcare costs. Golden Staph is a major cause of hospital-acquired infections in Australia and globally. The problem is largely due to the presence in hospitals of strains that are resistant to most clinically-useful antibiotics and are therefore very difficult to eradicate; the recent isolation of strains highly-resistant to one of the last resort anti-staphylococcal antibiotics, vancomycin, is particularly worrying. The emergence of these multiresistant strains is primarily attributable to the acquisition of pre-existing resistance determinants by cell-to-cell gene transfer, a process in which plasmids, extra-chromosomal DNA elements, play a prominent role. Staphylococcal multiresistance plasmids carry genes that can confer resistance to up to 20 antimicrobial agents and are themselves capable of transfer between bacterial cells. In this project, we will define the molecular mechanisms by which staphylococcal multiresistance plasmids efficiently replicate in the host cell and are stably maintained in growing bacterial populations or when acquired by a new host after transfer; such mechanisms may well provide novel drug targets. The results will also lead to the development of improved methods for the characterisation of clinical strains and the monitoring of antibiotic resistance, and will be of broad relevance to the problem of antimicrobial resistance in bacterial pathogens. Most importantly, the application of knowledge arising from these studies to the design and implementation of rational antibiotic usage policies has the potential to extend the efficacy of existing and future anti-staphylococcal therapies.