[A study on the disc sensitivity test for cefodizime].

Susceptibilities of 289 strains of 34 bacterial species to cefodizime (CDZM) were determined using the 2-fold agar dilution method in parallel with the measurement of inhibition zone diameters in the single-disc method under the experimental conditions established by Kanazawa. The experiments demonstrated a significant correlation between MIC by the dilution method and diameter of inhibition zone in each of the conventional, overnight assay (about 16 hours incubation), thus the applicability of the single-disc assay for CDZM was established. Analysis of the data obtained using discs containing 30 micrograms of CDZM/disc revealed that the primary regression equation was in the form: D (Diameter, mm) = 32.3-13.5 log MIC (micrograms/ml) in the conventional assay for staphylococci, Enterococcus group and glucose-non-fermentative Gram-negative rods. For other bacteria, the primary regression equation was in the form: D (diameter, mm) = 24.1-8.4 log MIC (micrograms/ml) in the conventional assay. The range of variations in MICs estimated from diameters of inhibition zones in the disc test was then calculated in comparison with that in MIC determined by the 2-fold agar dilution test to estimate experimental errors which may be involved in the determination of MICs of CDZM using the single-disc assay.