[A study on the disc sensitivity for ceftizoxime].

Abstract

Susceptibilities of 175 strains of 27 bacterial species to ceftizoxime (CZX) were determined by the 2-fold agar dilution method in parallel with the diameter of inhibition zones by 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 assay of over-night (about 16 hours) incubation, the delayed assay (about 24 hours incubation), and the rapid assay (about 3 approximately 4 or 5 approximately 6 hours incubation), thus confirming the applicability of the single-disc assay for CZX. Analysis of the data obtained by using CZX disc containing 30 micrograms revealed the primary regression equation to be: D (diameter, mm) = 27.3-9.7 log MIC (micrograms/ml) in conventional assay, D = 32.5-12.3 log MIC (micrograms/ml) in delayed assay, D = 22.8-7.5 log MIC (micrograms/ml) in 5 approximately 6 hours rapid assay, and D = 17.9-5.1 log MIC (micrograms/ml) in 3 approximately 4 hours rapid assay, respectively. The range of variations in MICs estimated from the diameter of inhibition zone by the disc test was then calculated in comparison with that in MIC determined by the 2-fold agar dilution test, as a reference for the experimental errors which may be involved in the estimation of MIC of CZX by the single-disc assay.