Background: Enterococci have become increasingly predominant as causative agents of nosocomial infections. Infections due to multi-drug resistant enterococci have drawn increasing attention during the past two decades. The purpose of the present study was to evaluate the occurrence of virulence factors and antimicrobial resistance in enterococci isolated from patients with bacteremia or urinary tract infection. 

Methods: A total of 209 strains of enterococi (102 Enterococcus faecalis and 107 E. facium) isolated during 8 months of 2005 were collected from 10 university hospitals in Korea. Disk diffusion susceptibility tests were performed using Mueller-Hinton agar. The antimicrobial resistance genes and virulence factors were determined using PCR. 

Results: In E. faecalis, the rate of resistance to ciprofloxacin, tetracycline, and quinupristindalfopristin was 27.4%, 83.3%, and 85.2%, respectively; no isolates were resistant to ampicillin, vancomycin, teicoplanin, or linezolid. In E. faecium, the rate of resistance to ampicillin, ciprofloxacin, tetracycline, vancomycin, and teicoplanin was 86.9%, 87.9%, 8.4%, 19.6%, and 6.5%, respectively; no strains were resistant to quinupristin-dalfopristin or linezolid. All the E. faecalis strains tested were found to harbor multiple virulence factors, but E. faecium strains were generally without virulence factors except esp. The prevalence of the esp gene was significantly higher in enterococci isolated from urinary tract infection than in those from bacteremia. 

Conclusion: A similar pattern of resistance to antimicrobial agents and prevalence of virulence factors was observed in both the enterococci isolated from bacteremia and urinary tract infection. Our study indicates that host factors are more likely than bacterial properties to influence the development of bacteremia. (Korean J Clin Microbiol 2006;9(2):77-83)