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Interpretive criteria for disk diffusion tests using 5-microgram cefdinir disks with rapidly growing clinical
R N Jones1, M E Erwin, B B Gooding
1Department of Pathology, University of Iowa College of Medicine, Iowa City 52242.
Journal of Clinical Microbiology
|April 1, 1992
Summary
This study evaluated cefdinir disk diffusion test criteria, finding high agreement but potential errors in Enterobacter species. Caution is advised for clinical labs using this method with Enterobacter isolates.
Area of Science:
- Clinical microbiology
- Antimicrobial susceptibility testing
Background:
- Disk diffusion tests are common for determining antibiotic susceptibility.
- Cefdinir is a widely used cephalosporin antibiotic.
- Establishing accurate interpretive criteria for disk diffusion tests is crucial for effective treatment.
Purpose of the Study:
- To establish preliminary interpretive zone diameter criteria for the 5-micrograms cefdinir disk diffusion test.
- To evaluate the agreement and error rates of proposed cefdinir disk diffusion criteria.
Main Methods:
- Calculation of zone diameter criteria using two minimum inhibitory concentration (MIC) breakpoints (≤0.5 and ≤1 µg/ml).
- Assessment of absolute agreement and identification of sources of false-susceptibility errors.
- Proposal of specific zone diameter criteria for susceptibility (≥20 mm) and resistance (≤16 mm).
Main Results:
- Absolute agreement between tests ranged from 85.9% to 92.4%.
- Enterobacter species were the primary source of false-susceptibility errors (2.2%).
- Proposed criteria: ≥20 mm zone for susceptibility (≤1 µg/ml MIC) and ≤16 mm zone for resistance (>2 µg/ml MIC).
Conclusions:
- The proposed cefdinir disk diffusion criteria show good overall agreement but require careful application.
- Clinical laboratories must be aware of potential major interpretive errors, particularly with Enterobacter isolates.
- Further validation is recommended to refine cefdinir disk diffusion testing for Enterobacter species.