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High-level aminoglycoside resistance in enterococci
J Gutiérrez1, A Hoyos, G Piedrola
1Departamento de Microbiologia, Hospital Universitario San Cecilio, Universidad de Granada, Spain.
Abstract:
In recent years enterococci have been isolated with increasing frequency in association with serious infections. Suitable therapy for empirical treatment can only be chosen on the basis of susceptibility studies. The synergistic effects obtained by the combination of aminoglycosides with penicillin or vancomycin disappear in strains that show high level resistance (HLR) to the former. This highlights the importance of correct identification of the species of Enterococcus (especially Enterococcus faecium, a particularly resistant species), and of studies designed to examine HLR in severe infections. The preferred methods are dilution in solid or liquid medium with 2,000 micrograms of aminoglycoside per ml, or diffusion in solid medium from discs impregnated with 120 micrograms of gentamicin (which also predicts the microorganism's susceptibility to tobramycin and netilmicin) or kanamycin (which also predicts the response to amikacin), and 300 micrograms of streptomycin, for Enterococcus faecalis. The reliability of automated systems for the prediction of HLR to aminoglycosides has yet to be assessed.
Insights
High-level aminoglycoside resistance (HLR) in enterococci complicates treatment of serious infections. Susceptibility testing is crucial for selecting effective empirical therapies, especially for resistant strains like Enterococcus faecium.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Enterococci are increasingly implicated in severe human infections.
- Empirical antibiotic therapy requires accurate antimicrobial susceptibility data.
- High-level aminoglycoside resistance (HLR) negates synergistic effects of combination therapies (aminoglycosides with penicillin or vancomycin).
Purpose of the Study:
- To emphasize the importance of accurate Enterococcus species identification, particularly Enterococcus faecium.
- To highlight the necessity of studying HLR in enterococcal infections.
- To outline reliable methods for detecting HLR to aminoglycosides.
Main Methods:
- Standardized dilution methods using 2,000 µg/mL of aminoglycoside in solid or liquid media.
- Disk diffusion methods with specific gentamicin (120 µg) or streptomycin (300 µg) disks for Enterococcus faecalis.
- Gentamicin disk diffusion predicts resistance to tobramycin and netilmicin; kanamycin disk diffusion predicts resistance to amikacin.
Main Results:
- Specific methodologies are recommended for detecting HLR in enterococci.
- Certain disk diffusion tests can predict cross-resistance to multiple aminoglycosides.
Conclusions:
- Accurate identification and HLR testing of enterococci are critical for effective patient management.
- Established dilution and disk diffusion methods provide reliable detection of HLR.
- Further evaluation is needed for automated systems in predicting HLR to aminoglycosides.