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Criteria for disk susceptibility tests and quality control guidelines for the cefoperazone-sulbactam combination
Abstract:
For in vitro susceptibility tests with cefoperazone and sulbactam (a beta-lactamase inhibitor), 75/30-micrograms disks may be used with the interpretive zone size breakpoints that are currently used for 75-micrograms cefoperazone disks. For dilution tests, a 2:1 ratio of cefoperazone to sulbactam is recommended. For quality control purposes, MIC limits that are used to monitor cefoperazone tests were also applied to tests with the combination of drugs. For gram-negative control strains, zone size limits were calculated to be 1 mm smaller than those used for cefoperazone disks. To monitor the sulbactam portion of the combination, Acinetobacter calcoaceticus subsp. anitratus ATCC 43498 was selected; zones with 75/30-micrograms disks were 26 to 32 mm in diameter, and broth microdilution MICs ranged from 1.0/0.5 to 8.0/4.0 micrograms/ml. With cefoperazone alone, MICs for Acinetobacter calcoaceticus subsp. anitratus were 16 to 64 micrograms/ml and zones ranged from 14 to 18 mm in diameter. For anaerobic dilution tests, only Bacteroides thetaiotaomicron ATCC 29741 is recommended for cefoperazone-sulbactam; MICs ranged from 8.0/4.0 to 32/16 micrograms/ml.
Insights
This study establishes guidelines for in vitro susceptibility testing of cefoperazone and sulbactam. Recommended disk diffusion and dilution methods ensure accurate antimicrobial susceptibility testing for this combination drug.
Area of Science:
- Microbiology
- Clinical Pharmacy
- Antimicrobial Resistance
Background:
- Cefoperazone, a beta-lactam antibiotic, is often combined with sulbactam, a beta-lactamase inhibitor, to broaden its spectrum of activity.
- Standardized in vitro susceptibility testing methods are crucial for guiding appropriate antimicrobial therapy.
Purpose of the Study:
- To define optimal in vitro susceptibility testing methodologies for the combination of cefoperazone and sulbactam.
- To establish quality control parameters for reliable testing.
Main Methods:
- Disk diffusion tests using 75/30-microgram disks with existing cefoperazone breakpoints.
- Broth microdilution tests recommending a 2:1 ratio of cefoperazone to sulbactam.
- Quality control using established MIC limits for cefoperazone and specific control strains.
Main Results:
- Disk diffusion zone size limits for gram-negative strains were adjusted by -1 mm compared to cefoperazone alone.
- Acinetobacter calcoaceticus subsp. anitratus ATCC 43498 was validated as a quality control strain for the sulbactam component.
- Bacteroides thetaiotaomicron ATCC 29741 was identified as the recommended anaerobic control strain.
Conclusions:
- The proposed methods provide a reliable framework for in vitro susceptibility testing of cefoperazone-sulbactam.
- Standardized testing ensures accurate interpretation of results for clinical decision-making.