[A study of the disc sensitivity test for cephapirin]

Susceptibility of 203 strains of 34 bacterial species or subspecies to cephapirin (CEPR) was determined by the 2-fold agar dilution method in parallel with the determination of inhibition zone diameter in the single-disc method. These experiments demonstrated a significant correlation between the MIC by the dilution method and the diameter of inhibition zone determined by the conventional assay using an over-night (about 16 hours) incubation, the delayed assay (about 24 hours incubation), or the rapid assay (after 3-4 or 5-6 hours incubation), hence applicability of the single-disc assay for CEPR was confirmed. An analysis of the data obtained using CEPR discs (each containing 30 micrograms) revealed that primary regression equations were as follows: D (diameter, mm) = 25.8-9.7 log MIC (microgram/ml) in the conventional assay; D = 31.2-12.3 log MIC in the delayed assay; D = 21.7-7.1 log MIC in the 5-6-hour rapid assay and D = 17.9-5.0 log MIC in the 3-4-hour rapid assay, and especially for beta-lactamase producing Staphylococci, they were: D = 24.9-9.2 log MIC in the conventional assay, D = 20.4-7.4 log MIC in the 5-6-hour rapid assay and D = 17.5-5.8 log MIC in the 3-4-hour rapid assay.(ABSTRACT TRUNCATED AT 250 WORDS)