Enterococcus

MICROBIOLOGY

• Enterococci facultatively anaerobic, gram-positive cocci in short chains; may grow under extreme conditions, i.e., 6.5% NaCl, pH 9.6, temp range from 10-45°C, and in the presence of bile salts.
  • Found in soil, water, food, and are significant component of normal colonic flora.
  • Also present in oropharyngeal and vaginal secretions.
• Relatively low virulence. Adheres to extracellular matrix proteins, urinary tract epithelia, and produces biofilms.
  
  • At times, capable of inciting sepsis and septic shock, especially in severely ill pts.
• Intrinsically resistant to many beta-lactams (e.g., cephalosporins) due to inner cell wall penicillin-binding proteins.
  
  • High level beta-lactam resistance is increasing in E. faecium, but uncommon in E. faecalis.
  • Resistant to TMP-SMX as organism uses exogenous folate to overcome anti-folate synthesis mechanism.
• Relatively impermeable to aminoglycosides. Adequate drug concentrations may be achieved with addition of a cell-wall agent and result in 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 genogroup^[1].
  • Use of vancomycin and anti-anaerobic antibiotics (broad-spectrum) risk factors for acquisition.