Methicillin-resistant Staphylococcus aureus: related infections and antibiotic resistance.

Staphylococcus aureus is a well adapted human pathogen, capable of living freely in the inanimate environment and spreading from person to person, existing as a colonizer or commensal, hiding in intracellular compartments and, most importantly, inducing various forms of human disease. Infections caused by S. aureus, above all by antibiotic-resistant strains, have reached epidemic proportions globally. The overall burden of staphylococcal disease caused by antibiotic-resistant S. aureus, particularly by the methicillin-resistant strains, is increasing in many countries, including Italy, in both healthcare and community settings. The widespread use of antibiotics has undoubtedly accelerated the evolution of S. aureus, which, acquiring multiple resistance genes, has become able to survive almost all antibiotic families; this evolution versus more resistant phenotypes has continued among the newer agents, including linezolid and daptomycin. The diminished clinical usefulness of vancomycin is seen as one of the most worrisome problems in many clinical settings and in many countries. In fact, the increasing spread of heteroresistant vancomycin-intermediate S. aureus (hVISA) and vancomycin intermediate (VISA) strains adds new problems, not only in terms of the treatment of severe infections sustained by these microorganisms, but also in the microbiological definition of susceptibility.