Analysis of Clonality and Antibiotic Resistance among Early Clinical Isolates ofEnterococcus faeciumin the United States

Abstract

BackgroundThe Enterococcus faecium genogroup, referred to as clonal complex 17 (CC17), seems to possess multiple determinants that increase its ability to survive and cause disease in nosocomial environments MethodsUsing 53 clinical and geographically diverse US E. faecium isolates dating from 1971 to 1994, we determined the multilocus sequence type; the presence of 16 putative virulence genes (hyl_Efm, esp_Efm and fms genes); resistance to ampicillin (AMP) and vancomycin (VAN); and high-level resistance to gentamicin and streptomycin ResultsOverall, 16 different sequence types (STs), mostly CC17 isolates, were identified in 9 different regions of the United States. The earliest CC17 isolates were part of an outbreak that occurred in 1982 in Richmond, Virginia. The characteristics of CC17 isolates included increases in resistance to AMP, the presence of hyl_Efm and esp_Efm emergence of resistance to VAN, and the presence of at least 13 of 14 fms genes. Eight of 41 of the early isolates with resistance to AMP, however, were not in CC17 ConclusionsAlthough not all early US AMP isolates were clonally related, E. faecium CC17 isolates have been circulating in the United States since at least 1982 and appear to have progressively acquired additional virulence and antibiotic resistance determinants, perhaps explaining the recent success of this species in the hospital environment