DETECTION OF HIGH-LEVEL AND MODERATELY HIGH-LEVEL RESISTANCE TO GENTAMICIN AND STREPTOMYCIN IN ENTEROCOCCUS-FAECIUM BY A DISC DIFFUSION METHOD

We evaluated an agar disc diffusion test for the detection of high-lev el (greater than or equal to 2000 mg/L) and moderately high-level resi stance to gentamicin (MIC, greater than or equal to 128-less than or e qual to 1024 mg/L) and streptomycin (MIC, greater than or equal to 256 -less than or equal to 1024 mu g/ml) with 70 clinical isolates of Ente rococcus faecium. Results obtained using disks containing 120 mu g gen tamicin and 300 mu g streptomycin were compared with MICs determined b y an agar dilution method. Based on the scattergrams, the closest zone diameter correlations with MIC breakpoints were as follows: susceptib le, greater than or equal to 16 mm; and resistant, less than or equal to 10 mm, for both streptomycin and gentamicin. No major or very major errors were found with either aminoglycoside using these values. We c onclude that agar disk diffusion test can be used to accurately detect high-level or moderately high-level gentamicin and streptomycin resis tance in E. faecium.