text: ACME are not common among antibiotic sensitive S. aureus (MSSA).  The elements for the most prominent MRSA ACME appear to have assembled recently in S. epidermidis into the speG-positive ACME which was transferred to virulent S. aureus during the evolution of the epidemic USA300 MRSA strain.  This broadened the ability of S. aureus to colonize sites other than a specific part of the nose.  This strain is able to persist on intact skin and is spread rapidly person-to-person.  As a result, the speG-positive ACME is a particularly important element of MRSA pathogenesis.