Risk factors associated with ampicillin resistance in patients with bacteraemia caused by Enterococcus faecium

J Antimicrob Chemother. 2002 Dec;50(6):1003-9. doi: 10.1093/jac/dkf216.


Epidemiological characteristics of ampicillin-resistant, vancomycin-susceptible Enterococcus faecium are not well known. Recently, these strains have been proposed as the substratum for the later appearance of vancomycin-resistant E. faecium. To analyse this problem, the medical charts of patients with bacteraemia caused by E. faecium diagnosed in our institution during a 6 year period (1994-1999) were reviewed. Demographic data, clinical characteristics, antibiotic exposure and outcome were compared among patients with ampicillin-resistant (MIC > 16 mg/L, NCCLS criteria) and ampicillin-susceptible strains. Clonality between different strains was analysed by pulsed-field gel electrophoresis (PFGE). We evaluated 49 cases of E. faecium bacteraemia; 29 patients with ampicillin-resistant strains and 20 patients with -susceptible strains were identified. By logistic regression analysis, only previous administration of beta-lactams (OR: 6.3; 95% CI: 1.12-20.0) and urinary catheterization (OR:4.2; 95% CI: 1.3-30.0) were identified as predictors of ampicillin resistance in enterococcal bacteraemic patients. An elevated APACHE II score was the only independent factor associated with mortality in enterococcal bacteraemia (OR:13.5; 95% CI: 1.04-175.4). PFGE analysis revealed a strong association between specific ampicillin-resistant clones and the location of patients during hospitalization, suggesting nosocomial transmission. Bacteraemia caused by ampicillin-resistant enterococci was not associated with increased mortality when compared with bacteraemias caused by ampicillin-susceptible strains.

Publication types

  • Comparative Study

MeSH terms

  • Ampicillin Resistance*
  • Anti-Bacterial Agents / adverse effects
  • Anti-Bacterial Agents / therapeutic use
  • Bacteremia / drug therapy*
  • Bacteremia / microbiology
  • Chi-Square Distribution
  • Confidence Intervals
  • Enterococcus faecium / drug effects*
  • Enterococcus faecium / isolation & purification
  • Humans
  • Lactams
  • Logistic Models
  • Multivariate Analysis
  • Odds Ratio
  • Retrospective Studies
  • Risk Factors
  • Urinary Catheterization / adverse effects


  • Anti-Bacterial Agents
  • Lactams