- 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.
- Use of vancomycin and anti-anaerobic antibiotics (broad-spectrum) risk factors for acquisition.
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