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In vitro susceptibility studies of vancomycin-resistant Enterococcus faecalis
D F Sahm1, J Kissinger, M S Gilmore
1Clinical Microbiology Laboratory, University of Chicago, Illinois 60637-1463.
Antimicrobial Agents and Chemotherapy
|September 1, 1989
Summary
New Enterococcus faecalis strains show vancomycin resistance but remain susceptible to teicoplanin. This resistance impacts combination therapies and requires improved susceptibility testing methods for accurate detection.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Enterococcus faecalis is a common cause of hospital-acquired infections.
- Vancomycin is a critical antibiotic for treating serious enterococcal infections.
- Emergence of vancomycin-resistant Enterococcus faecalis (VRE) poses a significant public health threat.
Purpose of the Study:
- To describe a novel vancomycin resistance profile in Enterococcus faecalis isolates.
- To evaluate the impact of vancomycin resistance on the efficacy of combination antimicrobial therapies.
- To assess the reliability of different antimicrobial susceptibility testing methods for detecting vancomycin resistance in E. faecalis.
Main Methods:
- Phenotypic characterization of vancomycin resistance in E. faecalis isolates V583, V586, and V587.
- Determination of minimum inhibitory concentrations (MICs) for vancomycin and teicoplanin.
- Time-kill kinetic studies to evaluate the synergistic activity of vancomycin-aminoglycoside combinations.
- Comparison of various susceptibility testing methods including broth micro/macrodilution, agar dilution, disk-agar diffusion, and automated systems.
Main Results:
- Enterococcus faecalis isolates V583, V586, and V587 exhibited high-level vancomycin resistance (MICs 32–64 µg/ml).
- These isolates remained susceptible to teicoplanin (MIC ≤ 0.5 µg/ml), a unique glycopeptide susceptibility profile for E. faecalis.
- Vancomycin resistance diminished the synergistic activity of vancomycin-aminoglycoside combinations.
- Broth microdilution, broth macrodilution, and agar dilution methods reliably detected vancomycin resistance, while disk-agar diffusion and the Vitek AutoMicrobic system did not.
Conclusions:
- A novel glycopeptide susceptibility profile (vancomycin resistance, teicoplanin susceptibility) has been identified in E. faecalis.
- Vancomycin resistance in E. faecalis compromises the effectiveness of standard combination therapies.
- Current susceptibility testing methods require refinement to ensure reliable detection of vancomycin resistance in E. faecalis.