NEW HIGH-CONTENT DISKS FOR DETERMINATION OF HIGH-LEVEL AMINOGLYCOSIDE RESISTANCE IN CLINICAL ISOLATES OF ENTEROCOCCUS-FAECALIS

Disks impregnated with 500 and 1000-mu-g of streptomycin, 1000-mu-g of kanamycin and 250 and 500-mu-g of gentamicin were used for detection of high-level resistance to aminoglycosides in 120 clinical isolates of Enterococcus faecalis. Fifty-seven strains were highly resistant to streptomycin, 80 to kanamycin and 41 to gentamicin. Using disks containing 500-mu-g of streptomycin, 1000-mu-g of kanamycin and 500-mu-g 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-mu-g streptomycin or gentamicin disk. Zone-size breakpoints are proposed for detection of high-level resistance by disk diffusion.