CLONAL DISSEMINATION OF VANCOMYCIN-RESISTANT ENTEROCOCCI AND COMPARISON OF SUSCEPTIBILITY TESTING METHODS

One hundred fifty clinical isolates of Enterococcus faecalis (88 isola tes) and Enterococcus faecium 162 isolates) were tested in vitro for t heir susceptibility to vancomycin and high-level aminoglycosides (HLA) . Remel's Synergy Quad Plates (RSQ) were used as the reference method and compared to Kirby-Bauer disc diffusion test, Vitek(R) GPS-TA card, A MicroScan(R) Panel (GP-GI, and Etest(R). Streptomycin susceptibilit y results for MicroScan GP-6 and RSQ were recorded at 24 and 48 h and all other methods and antibiotics were lead at 24 it or less. When com pared with the agar screen method, all of the methods demonstrated >99 % agreement. One isolate Ic,as falsely sensitive to gentamicin at 24 h , but resistant at 48 it, when tested on both MicroScan and RSQ agar s creen. Thirty-nine isolates showed resistance to vancomycin with all m ethods. These isolates were from three different local hospitals and w ere identified as E. faecium. Pulse-field gel electrophoresis demonstr ated that all of the vancomycin-resistant isolates were derived from t he same clone. Of interest is the observation that high-level resistan ce to aminoglycosides varied between the clonally related isolates. (C ) 1998 Elsevier Science Inc.