Cefoperazone: spectrum of antibacterial activity and disc diffusion testing

Cefoperazone is a new cephalosporin with a very wide spectrum of antibacterial activity, including Enterobacteriaceae, Pseudomonas aeruginosa, staphylococci, streptococci (other than serological group D strains), Neisseria and Haemophilus species (including beta-lactamase positive strains) and some anaerobes. On testing more than 8700 clinical isolates, approximately 93% were inhibited by 16 micrograms/ml of cefoperazone, 95% by 32 micrograms/ml and 98% by 64 micrograms/ml. The drug is less active on Acinetobacter and group D streptococci. We recommend that a disc containing 75 micrograms of cefoperazone be used in the diffusion test with 'breakpoints' of less than or equal to 14 mm for resistant, 15-17 mm for intermediate, and greater than or equal to 18 mm for susceptible bacteria.