Tentative interpretive standards for agar disk diffusion antimicrobial susceptibility testing of cefoperazone

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Abstract
Cefoperazone is a new cephalosporin with a very wide spectrum of activity, including activity against Pseudomonas aeruginosa. It has less activity on enterococci and Acinetobacter. Of the 459 selected bacterial strains tested, only 1.5% (7 strains and 6 genera) had minimum inhibitory concentrations [MIC] of .gtoreq. 128 .mu.g/ml. For a MIC breakpoint of .ltoreq. 32 .mu.g/ml (susceptible), the disk diffusion test probably should be done with a 75-.mu.g disk and breakpoints of .gtoreq. 18 mm for susceptible, 15-17 mm for intermediate and .ltoreq. 14 mm for resistant. Diffusion tests using these criteria yielded only 1.1% very major or major errors.