High-Level Antibiotic Tolerance of a Clinically Isolated Enterococcus faecalis Strain

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacteria develop antibiotic resistance through gene acquisition or phenotypic tolerance.
• Multidrug-tolerant strains of *Enterococcus faecalis* pose a challenge in treating nosocomial infections.
• Tolerance involves phenotypic changes and reduced metabolic activity, distinct from resistance.

Purpose of the Study:

• To investigate a novel *Enterococcus faecalis* strain (UM001B) exhibiting high-level multidrug tolerance.
• To elucidate the molecular mechanisms underlying this observed tolerance.
• To understand the implications for treating *Enterococcus faecalis* infections.

Main Methods:

• Isolation and characterization of *E. faecalis* UM001B from a cystic fibrosis patient.
• Antibiotic susceptibility testing for ampicillin, vancomycin, and tetracycline.
• Whole-genome sequencing and comparative analysis with a reference strain (ATCC 29212).
• Molecular simulations and experimental assays to validate mutation effects.
• Replication of mutations in *Escherichia coli* to assess functional impact.

Main Results:

• *E. faecalis* UM001B showed high tolerance to ampicillin, vancomycin, and tetracycline without increased resistance.
• Reduced antibiotic penetration (ampicillin, vancomycin) and altered accumulation (tetracycline) were observed.
• Whole-genome sequencing identified four amino acid substitutions in a tetracycline efflux pump repressor (TetR).
• These mutations were linked to increased tetracycline efflux activity and tolerance.
• Introducing these mutations into *E. coli* enhanced its tetracycline tolerance.

Conclusions:

• The study identifies specific genetic mutations in TetR as a key mechanism for multidrug tolerance in *E. faecalis*.
• These findings offer new insights into the development of antibiotic tolerance in this pathogen.
• Understanding these mechanisms can aid in developing strategies to combat enterococcal infections more effectively.