Abstract
For a long time, Enterococcus faecium (E. faecium) was thought to be a commensal strain in human and animal digestive tracts. However, over the past three decades, some unique E. faecium clones rapidly acquired multiple antimicrobial resistance (AMR), which led these clones to survive hospital environments and become a hospital-adapted E. faecium clonal complex (CC) 17. Since the adaptation of these clones to changes in habitat, vancomycin-resistant E. faecium CC17 has emerged as the leading cause of hospital-acquired infections worldwide. This epidemic hospital-adapted lineage has diverged from other populations approximately 75 years ago. The CC17 lineage originated from animal strains, but not human commensal lines. We reviewed the evolutionary progress and the molecular mechanisms of E. faecium CC17 from a gut commensal to a multi-antimicrobial resistant nosocomial pathogen.