Enterococcus

Lisa A. Spacek, M.D., Ph.D.
Enterococcus is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • Enterococci are facultatively anaerobic Gram-positive bacteria in short chains, which 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.
    • Comprise a significant component of normal colonic flora
    • Found in oropharyngeal and vaginal secretions
    • Isolated from soil, water, food
    • They are not as intrinsically virulent as Staphylococcus aureusor Streptococcus pyogenes.
  • Adhere to extracellular matrix proteins and urinary tract epithelia.
    • Produces biofilms.
    • It exploits the opportunity to proliferate once antibiotic-susceptible organisms are eradicated.
  • Antimicrobial resistance attributes[9]
    • Species-specific differences
      • High-level β-lactam resistance is increasing in E. faecium but is uncommon in E. faecalis.
    • Intrinsic resistance to many β-lactams (e.g., cephalosporins) due to inner cell wall penicillin-binding proteins.
    • Resistance to TMP/SMX as enterococci use exogenous folate to overcome the anti-folate synthesis mechanism.
    • Relative impermeability to aminoglycosides (AG), adding a cell-wall agent may allow bactericidal effect at ribosomal target.
      • Ribosomal mutation and decreased aminoglycoside transport confer high-level AG resistance.
      • Some gentamicin-resistant strains may remain susceptible to streptomycin.
  • Vancomycin-resistant enterococci (VRE): occurs E. faecium >>> E. faecalis.[10]
    • Plasmid-mediated VanA and VanB gene complexes confer high-level vancomycin resistance.
    • Increased incidence of vancomycin-resistantE. faecium attributed to the emergence of clonal cluster 17 (CC17) genogroup, CC17 is most common.[17]

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MICROBIOLOGY

  • Enterococci are facultatively anaerobic Gram-positive bacteria in short chains, which 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.
    • Comprise a significant component of normal colonic flora
    • Found in oropharyngeal and vaginal secretions
    • Isolated from soil, water, food
    • They are not as intrinsically virulent as Staphylococcus aureusor Streptococcus pyogenes.
  • Adhere to extracellular matrix proteins and urinary tract epithelia.
    • Produces biofilms.
    • It exploits the opportunity to proliferate once antibiotic-susceptible organisms are eradicated.
  • Antimicrobial resistance attributes[9]
    • Species-specific differences
      • High-level β-lactam resistance is increasing in E. faecium but is uncommon in E. faecalis.
    • Intrinsic resistance to many β-lactams (e.g., cephalosporins) due to inner cell wall penicillin-binding proteins.
    • Resistance to TMP/SMX as enterococci use exogenous folate to overcome the anti-folate synthesis mechanism.
    • Relative impermeability to aminoglycosides (AG), adding a cell-wall agent may allow bactericidal effect at ribosomal target.
      • Ribosomal mutation and decreased aminoglycoside transport confer high-level AG resistance.
      • Some gentamicin-resistant strains may remain susceptible to streptomycin.
  • Vancomycin-resistant enterococci (VRE): occurs E. faecium >>> E. faecalis.[10]
    • Plasmid-mediated VanA and VanB gene complexes confer high-level vancomycin resistance.
    • Increased incidence of vancomycin-resistantE. faecium attributed to the emergence of clonal cluster 17 (CC17) genogroup, CC17 is most common.[17]

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Last updated: November 9, 2022