DETECTING ERYTHROMYCIN RESISTANCE IN STREPTOCOCCUS-PYOGENES - RELIABILITY OF THE DISK DIFFUSION METHOD AND THE BREAKPOINT SUSCEPTIBILITY TESTING METHOD

Erythromycin susceptibility of clinical Streptococcus pyogenes isolate s was determined at 19 Finnish clinical microbiology laboratories by t heir routine disk diffusion method and by a screening method adapted f rom the breakpoint susceptibility testing method. Results obtained at 12 laboratories using 4 major variants of the disk method were further evaluated. From these laboratories, 286 consecutive resistant and 349 consecutive susceptible isolates were sent to the Antimicrobial Resea rch Laboratory, Turku where the MIC of erythromycin was determined. 96 % and 97% of the disk results were correct, as compared with MIC resul ts, when general and laboratory-specific breakpoints, respectively, we re used, The results of the screening method were comparable to those of the disk method.