What is the percentage of Enterococcus faecalis resistant to linezolid?

Linezolid Resistance in Enterococcus Faecalis

Linezolid resistance in Enterococcus faecalis remains rare, with sustained susceptibility rates of approximately 99.8% according to surveillance programs. 1

Prevalence and Epidemiology

• The prevalence of linezolid resistance in Enterococcus faecalis is significantly lower than in other enterococcal species, with most surveillance programs reporting resistance rates below 1% 1
• In contrast to vancomycin resistance, which can be as high as 82.1% for E. faecalis according to the U.S. CDC's National Healthcare Safety Network, linezolid resistance remains uncommon 2
• Linezolid resistance is more frequently observed in healthcare-associated settings, particularly in patients with prolonged exposure to the antibiotic 3
• Some regional variations exist, with one study from a tertiary hospital in China reporting linezolid resistance/intermediate rates as high as 22.61% among E. faecalis isolates from urinary tract infections 4

Mechanisms of Resistance

• The primary mechanism of linezolid resistance in E. faecalis is the G2576T (also noted as G2576U) mutation in the 23S rRNA, which accounts for approximately 51.2% of resistant isolates 1, 5
• Additional resistance mechanisms include:
  • The cfr gene (present in approximately 4.7% of linezolid-resistant E. faecalis), which can transfer horizontally between strains 1
  • The optrA gene, which has been increasingly identified in resistant isolates, particularly in China 4, 6
  • The poxtA gene, often found alongside optrA and cfr-like variants in multi-resistant strains 6
• A gene dosage effect has been observed, where the number of mutated copies of 23S rRNA correlates with the level of resistance 5

Risk Factors for Developing Resistance

• Prior exposure to linezolid is the most significant risk factor, with a mean treatment duration of 29.8±48.8 days associated with the development of resistance in E. faecalis 1, 3
• Extended courses of linezolid therapy (>30 days) significantly increase the risk of resistance development 3
• Additional risk factors identified in clinical studies include:
  • Indwelling catheters 4
  • Tracheal cannulation 4
  • Prolonged hospitalization, particularly in intensive care settings 1

Clinical Implications

• For vancomycin-resistant E. faecalis infections, linezolid remains an important therapeutic option despite isolated cases of resistance 2, 7
• In patients who have recently received extended linezolid therapy and develop a new enterococcal infection, susceptibility testing should be performed promptly to guide therapy 3
• For patients with linezolid-resistant E. faecalis, alternative agents such as daptomycin (8-12 mg/kg/day) may be considered, particularly for bloodstream infections 2, 7
• For intra-abdominal infections with vancomycin-resistant E. faecalis that are also linezolid-resistant, tigecycline may be an appropriate alternative 2

Prevention Strategies

• Judicious use of linezolid, particularly avoiding prolonged courses when alternatives are available 3
• Implementation of antimicrobial stewardship programs to monitor linezolid use in healthcare settings 1
• Prompt identification and isolation of patients with linezolid-resistant enterococci to prevent horizontal transmission 6
• Regular surveillance of linezolid susceptibility patterns in clinical isolates, especially in high-risk settings 1