Is amoxicillin or linezolid effective against Enterococcus (E.) Faecalis biofilms?

Effectiveness of Amoxicillin and Linezolid Against E. faecalis Biofilms

For Enterococcus faecalis biofilms, amoxicillin shows limited effectiveness while linezolid combined with rifampicin demonstrates better activity, though neither is optimal as monotherapy for biofilm eradication. 1

Amoxicillin Effectiveness Against E. faecalis Biofilms

• Amoxicillin is recommended as a first-line treatment for enterococcal infections, but has poor biofilm penetration and limited effectiveness against established E. faecalis biofilms 1
• For enterococcal infections, ampicillin/amoxicillin is considered first choice for susceptible strains, but biofilm formation significantly reduces its effectiveness 1
• In vitro studies demonstrate that E. faecalis biofilms require extremely high concentrations of amoxicillin (MBIC90 of 8192 mg/L) for inhibition, which are not clinically achievable 2
• Tolerance to amoxicillin was observed in 93% of E. faecalis isolates growing in biofilms, indicating poor biofilm eradication capabilities 2

Linezolid Effectiveness Against E. faecalis Biofilms

• Linezolid alone has limited activity against E. faecalis biofilms, requiring very high concentrations (MBIC90 of 4096 mg/L) for inhibition 2
• Linezolid is recommended for ampicillin-resistant and vancomycin-resistant enterococci, but its toxicity profile may limit long-term use needed for biofilm eradication 1
• For enterococcal biofilm infections, linezolid demonstrates better tissue penetration than some alternatives, but still has limited biofilm activity as monotherapy 3
• Tolerance to linezolid was observed in 93% of E. faecalis isolates growing in biofilms 2

Combination Therapy Approaches

• The combination of linezolid with rifampicin significantly improves activity against E. faecalis biofilms, reducing the minimum biofilm eradication concentration to 16-32 mg/L 4
• Rifampicin must always be combined with a second agent (like linezolid) to reduce the likelihood of resistance emergence when treating biofilm infections 1, 5
• When linezolid is combined with rifampicin, development of rifampicin resistance is reduced compared to rifampicin monotherapy or rifampicin-ampicillin combinations 4
• Adding gentamicin to linezolid or amoxicillin has variable effects on biofilm activity and is not predictable by standard susceptibility testing 2

Clinical Implications and Treatment Recommendations

• For implant-associated infections with E. faecalis biofilms, thorough debridement is essential before antibiotic therapy to reduce bacterial load 1, 3
• In fracture-related infections with E. faecalis, ampicillin/amoxicillin is first choice for initial IV therapy, followed by oral amoxicillin, but may be insufficient for biofilm eradication 1
• For catheter-related bloodstream infections with E. faecalis biofilms, catheter removal is often necessary as antibiotic therapy alone may be insufficient 1
• If catheter retention is necessary in enterococcal infections, antibiotic lock therapy should be used in addition to systemic therapy 1
• For vancomycin-resistant E. faecalis biofilms, linezolid or daptomycin may be considered, with linezolid having better tissue penetration 1

Important Considerations and Pitfalls

• Long-term linezolid use is limited by toxicity concerns including myelosuppression, peripheral and optic neuropathy, and lactic acidosis 1, 3
• Ciprofloxacin monotherapy is not recommended against enterococci due to rapid emergence of resistance and high treatment failure rates 5
• In vitro studies show that erythromycin and oxytetracycline may have better activity against E. faecalis biofilms than amoxicillin or linezolid in some cases 6
• The combination of ciprofloxacin and rifampicin showed the most effective biofilm reduction in some in vitro studies, followed by linezolid and rifampicin 4
• Development of rifampicin resistance is a significant concern when treating E. faecalis biofilms with rifampicin-containing regimens 4, 7