Enterococcus

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]