Le infezioni da Staphylococcus aureus meticillino-resistente ed Enterococcus species vancomicino-resistente

Traditionally methicillin-resistant Staphylococcus aureus (MRSA) are considered a healthcare-associated pathogen in hospital patients (HA-MRSA), however is now emerging also in the community (CA-MRSA) without established risk factors. The emergence of MRSA is the acquisition of the mecA gene and associated mec DNA by methicillin-susceptible S. aureus and their integration into its chromosome. MRSA infections are associated with significant higher morbidity and mortality rates compared to MSSA. In USA >50% of hospital-acquired S. aureus isolates in intensive care units (ICU) are MRSA. In Europe, although there is a prevalent north-south gradient as MRSA strains are rare in Scandinavia (<5%) and more frequent in southern Europe (>40%), some variation between geographic areas remains unclear. Vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) are an emerging problem. The principal risk factors for MRSA acquisition are represented by: length of hospital stay, antimicrobial use (cephalosporin and chinolones), ICU, colonized patients. Since 80’ acquired resistance to glycopeptide of enterococci such as Enterococcus faecium and Enterococcus faecalis (VRE) was observed. In these species, several genes mediate resistance, the most common of which are vanA and vanB. The prevalence of VRE is variable across Europe and higher in USA. VRE infections are associated with significant higher morbidity and mortality rates compared to vancomycin-sensitive strains (VSE). Risk factors commonly associated are severe underlying diseases, prolonged hospital stay and previous antibiotic therapy