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
• 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 (AG), addition of 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.
  • 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.[10]