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

Area of Science:

• Microbiology
• Pharmacology
• Clinical Diagnostics

Background:

• Cefoperazone is a novel cephalosporin antibiotic.
• It exhibits a broad spectrum of activity, notably against Pseudomonas aeruginosa.
• Activity against enterococci and Acinetobacter is less pronounced.

Purpose of the Study:

• To evaluate the in vitro activity of cefoperazone against a diverse range of bacterial strains.
• To establish reliable disk diffusion test criteria for cefoperazone susceptibility testing.
• To assess the accuracy of proposed disk diffusion breakpoints.

Main Methods:

• Testing of 459 bacterial strains against cefoperazone.
• Determination of minimum inhibitory concentrations (MICs).
• Correlation of MICs with disk diffusion test results using a 75-microgram disk.

Main Results:

• Cefoperazone demonstrated broad-spectrum activity, with only 1.5% of strains showing high MICs (≥128 µg/ml).
• Recommended disk diffusion breakpoints are ≥18 mm (susceptible), 15–17 mm (intermediate), and ≤14 mm (resistant) for MICs ≤32 µg/ml.
• The proposed criteria resulted in a low error rate (1.1% very major or major errors).

Conclusions:

• Cefoperazone is an effective antibiotic against a wide array of bacteria, including Pseudomonas aeruginosa.
• The recommended disk diffusion test parameters are accurate for predicting cefoperazone susceptibility.
• These findings support the clinical utility of cefoperazone and standardized susceptibility testing methods.