[Comparison of the microdilution method (PASCO), the Etest and disc-diffusion in streptococcus pneumoniae antibiotic...

MIC values and inhibition zone diameters for penicillin, cefotaxime, and erythromycin where determined in 75 consecutive Streptococcus pneumoniae blood isolates by microdilution (PASCO), disc-diffusion and Etest. Using the Etest, 40% and 29.3% of the isolates showed low- or high-level resistance to penicillin and erythromycin respectively, whereas 9.3% were intermediate to cefotaxime. No high-level resistance to cefotaxime was found. No errors were found with the comparison of penicillin and cefotaxime results by microdilution and Etest, with just 2 (2.7%) and 3 (4%) minor errors appearing respectively. On the other hand, when comparing penicillin susceptibility results by disc-diffusion (1 mg oxacillin disc) and Etest, 6 (8%) major errors and 18 (24%) minor errors were found.