New high-content disks for determination of high-level aminoglycoside resistance in clinical isolates ofEnterococcus faecalis

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Abstract
Disks impregnated with 500 and 1000 µg of streptomycin, 1000 µg of kanamycin and 250 and 500 µg of gentamicin were used for detection of high-level resistance to aminoglycosides in 120 clinical isolates ofEnterococcus faecalis. Fifty-seven strains were highly resistant to streptomycin, 80 to kanamycin and 41 to gentamicin. Using disks containing 500 µg of streptomycin, 1000 µg of kanamycin and 500 µg of gentamicin strains resistant to high levels of these drugs (97.9 %, 100 % and 100 %, respectively) were accurately detected. Better discrimination between high-level and low-level resistance was achieved with a 500 µg streptomycin or gentamicin disk. Zone-size breakpoints are proposed for detection of high-level resistance by disk diffusion.