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Methicillin-resistant Staphylococcus aureus: an ever emerging threat

X Bertrand

Among multidrug-resistant bacteria, methicillin-resistant Staphylococcus aureus (MRSA) is of immediate concern, given its potential for pathogenicity and widespread presence in healthcare settings. Over the last four decades, MRSA has spread throughout the world and the global prevalence of MRSA in hospitals (hospital-associated MRSA) continues to increase with the dissemination of a limited number of MRSA clones, each with a specific genetic background and staphylococcal cassette chromosome mec. Measures to control the hospital spread of MRSA have concentrated principally on transmission-based control policies. European surveillance data suggest that the increasing rate of hospital-associated MRSA is not an inexorable trend, and European countries with variable baseline prevalence and infection control policies were able to reverse the MRSA trend. Recently, MRSA strains have emerged and rapidly spread in the community. These so-called community-associated (CA)‑MRSA strains are mainly associated with skin and soft tissue infections in previously healthy and young persons. CA‑MRSA isolates from different areas of the world have common characteristics: the production of Panton–Valentine leukocidin and the presence of short staphylococcal cassette chromosome mec elements. In the USA, CA‑MRSA became more prevalent than methicillin-susceptible S. aureus in community-associated S. aureus infections. In Europe, their prevalence remains below 5%, except for in Greece. The recent emergence of virulent CA‑MRSA isolates harboring the tst gene and of MRSA from animal origin is of major concern. Large efforts are necessary to avoid penicillinase-mediated resistance in S. aureus occuring again with MRSA.