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Antimicrobial Agents and Chemotherapy, July 2005, p. 2693-2700, Vol. 49, No. 7
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.7.2693-2700.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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

Departamento de Microbiología,¹ Departamento de Enfermedades Infecciosas, Hospital Universitario Ramón y Cajal, Madrid, Spain,³ Eijkman-Winkler Institute for Microbiology, Infectious Diseases and Inflammation,² Division of Acute Internal Medicine and Infectious Diseases, University Medical Center Utrecht, Utrecht, The Netherlands⁴

Received 29 November 2004/ Returned for modification 16 January 2005/ Accepted 4 March 2005

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.

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