The Evolution and Dynamics of Methicillin-Resistant Staphylococcus aureus

This chapter deals with the challenges in hospitals presented by the widespread occurrence of Methicillin-Resistant Staphylococcus aureus (MRSA), especially with the recent emergence of strains with intermediate susceptibility to glycopeptides and of community-acquired MRSA. Staphylococcus aureus is a Gram-positive bacterium which typically resides asymptomatically on the skin and in the nose of animals, and in particular of mammals. Since its discovery in the 1880s, it has been recognized as a major opportunistic pathogen in humans responsible for various diseases, ranging from minor skin infections to severe bacteraemia and necrotizing pneumonia. The introduction of penicillin in the early 1940s saved the lives of tens of thousands of wounded allied troops in the Second World War and dramatically improved the prognosis of patients with staphylococcal infections. Given the difficulties to control MRSA, a thorough understanding of the processes underlying the emergence and spread of MRSA may help designing new strategies to counteract this evolution. In the 50 years, community-associated MRSA (CA-MRSA) have continued to emerge and spread from the mid-1990s onwards. Perhaps the most interesting, and also worrying, example is the emergence of MRSA clones specific within the community. With the advance of recent sequencing technologies and development of associated bioinformatics tools, it will be possible to analyze and compare several genomes in a short period of time. These data will address many important questions about the evolution and epidemiology of MRSA and will bridge the gap left by the low discriminatory power of MLST. © 2011