Population Structure of Enterococcus faecium Causing Bacteremia in a Spanish University Hospital: Setting the Scene for a Future Increase in Vancomycin Resistance?

Abstract

ABSTRACT Over an 8-year period (1995 to 2002), 86 Enterococcus faecium blood isolates from 84 patients, of which 54 were ampicillin resistant (AREF) and 32 were ampicillin susceptible (ASEF), were studied in a university hospital (1,200 beds; serving a population of 600,000) in Spain, a country characterized by a near-absence of resistance to vancomycin and very high rates of ampicillin resistance among enterococci. Clonal relatedness by pulsed-field gel electrophoresis (PFGE), antibiotic susceptibility, presence of the virulence/epidemicity genes esp Efm and hyl Efm , and identification of purK alleles were studied. A group of isolates was also analyzed by amplified fragment length polymorphism (AFLP) and multilocus sequence typing. Medical charts (30 variables collected) were reviewed for 60/84 patients. ASEF showed high clonal diversity (32 PFGE types, 11 purK alleles, 4 AFLP genogroups), did not harbor putative virulence genes, and had no specific association with hospital acquisition. AREF isolates belonged to a clonal complex (CC) of genetically related strains ( purK - 1 , AFLP genogroup C), occasionally harboring putative virulence traits, and were from patients with particular risk factors. Within this CC, previously associated with vancomycin-resistant E. faecium isolates causing outbreaks worldwide (W. L. Homan et al., J. Clin. Microbiol. 40: 1963-1971, 2002), a great genetic diversity of antibiotic resistance and virulence/epidemicity profiles was found. Associations between esp and a >7-day hospital stay and between purK - 1 , hospital location, and nosocomial acquisition were noted ( P < 0.001). These findings reflect the importance of local environmental differences in the evolution of this CC, suggesting that the emergence of vancomycin resistance among AREF strains in Spain may be a question of time.