Johns Hopkins Antibiotic (ABX) Guide

Enterococcus

MICROBIOLOGY

  • Enterococci are facultative anaerobic, gram-positive bacteria in short chains; may grow under extreme conditions, i.e., 6.5% NaCl, pH 9.6, temperature range from 10-45°C, and in the presence of bile salts.
    • Significant component of normal colonic flora, present in oropharyngeal and vaginal secretions.
    • Found in soil, water, food.
  • Adheres to extracellular matrix proteins and urinary tract epithelia; produces biofilms.
    • Exploits opportunity to proliferate once antibiotic-susceptible organisms are eradicated.
    • High-level resistant strains of E. faecium infection associated with mortality of 30%.
  • Species-specific antimicrobial resistance differences, e.g., high-level β-lactam resistance is increasing in E. faecium, but uncommon in E. faecalis.
    • Intrinsically resistant to many β-lactams (e.g., cephalosporins) due to inner cell wall penicillin-binding proteins.
    • Resistant to TMP/SMX as organism uses exogenous folate to overcome anti-folate synthesis mechanism.
    • Relatively impermeable to aminoglycosides. Addition of a cell-wall agent may allow bactericidal effect at ribosomal target.
      • Ribosomal mutation and decreased aminoglycoside transport confer high-level resistance.
      • Some gentamicin-resistant strains may remain susceptible to streptomycin.
  • Vancomycin resistant enterococci (VRE): occurs E. faecium >>> E. faecalis.
    • Plasmid-mediated VanA and VanB gene complexes confer high-level vancomycin resistance.
    • Increased incidence of vancomycin resistant E. faecium attributed to emergence of clonal cluster 17 (CC17) genogroup, CC17 is most common[1].

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