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Determination of high level resistance to aminoglycosides among enterococci
B P Cherian1, E Mathai, S Chandy
1Department of Microbiology, Christian Medical College & Hospital, Vellore.
Abstract:
Two hundred and ten strains of enterococci showing resistance to gentamicin (10 micrograms/disc) were tested for high level resistance by detecting the minimum inhibitory concentration and by using high content disc diffusion test. Only 67 per cent of these had high level resistance to gentamicin. High level kanamycin resistance in the group was 84 per cent, while high level streptomycin resistance was 61 per cent. Only 85 of the 140 strains with high level gentamicin resistance had similar streptomycin resistance. Results using locally made high content discs, correlated 100 per cent with MIC results. High level resistance to enterococci should be reported on a routine basis, especially when isolated from patients with serious infections.
Insights
Many enterococci strains resistant to gentamicin are not highly resistant. High-level resistance testing is crucial for guiding treatment in serious infections, especially with aminoglycoside antibiotics.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Enterococci are significant nosocomial pathogens.
- Aminoglycoside antibiotics are vital for treating serious enterococcal infections.
- High-level aminoglycoside resistance (HLAR) in enterococci compromises treatment efficacy.
Purpose of the Study:
- To evaluate the prevalence of high-level gentamicin resistance (HLGR) in enterococci strains exhibiting gentamicin disc resistance.
- To assess high-level kanamycin resistance (HLKR) and high-level streptomycin resistance (HLSR) in the same isolates.
- To compare the accuracy of a high-content disc diffusion test with minimum inhibitory concentration (MIC) for detecting HLAR.
Main Methods:
- Two hundred and ten enterococcal strains with gentamicin disc resistance were tested.
- Minimum inhibitory concentrations (MICs) were determined.
- A high-content disc diffusion test was employed.
- Correlation between MIC results and disc diffusion tests was analyzed.
Main Results:
- Only 67% of gentamicin-resistant strains demonstrated high-level gentamicin resistance.
- High-level kanamycin resistance was observed in 84% of strains, and high-level streptomycin resistance in 61%.
- Locally manufactured high-content discs showed 100% correlation with MIC results.
Conclusions:
- A significant proportion of enterococci with gentamicin resistance do not possess high-level resistance.
- Routine reporting of high-level enterococcal resistance is recommended, particularly for isolates from severe infections.
- Accurate and accessible methods for detecting HLAR are essential for effective patient management.