- 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
- 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.
- 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.
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