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Comparison of methods for the interpretation of disk diffusion susceptibility tests for augmentin
Abstract:
Disk diffusion susceptibility tests for Augmentin were performed on 239 patients isolates. They were interpreted by means of Stoke's criteria, the ICS method, and a modified error minimization technique. A reference minimal inhibitory concentration of less than or equal to 16 mg/L was chosen to correspond to likely therapeutic success in urinary tract infection and the performance of each method was compared. Zone radii of inhibition correlated well with the minimal inhibitory concentration. A single urinary breakpoint for susceptibility could be established by means of the error minimization technique (Zs greater than or equal to 6 mm radius) which classified 1% of strains as falsely susceptible. The false-resistant rate, however, was increased to 14% and alternative test conditions are advised if true rates of resistance are to be determined. Use of an indeterminate category (4 less than Z1 less than 6 mm radius) is recommended when the rate of resistance is in excess of 20% but not otherwise.
Insights
Disk diffusion tests for Augmentin were evaluated for urinary tract infections. The error minimization technique established a reliable susceptibility breakpoint, though false resistance rates require attention for accurate resistance determination.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Pharmacology
Background:
- Disk diffusion susceptibility testing is crucial for guiding antibiotic therapy.
- Accurate interpretation of Augmentin (amoxicillin/clavulanate) susceptibility is vital for treating urinary tract infections (UTIs).
- Standardized methods are needed to reliably assess bacterial resistance patterns.
Purpose of the Study:
- To compare the performance of Stoke's criteria, ICS method, and a modified error minimization technique for Augmentin disk diffusion tests.
- To establish a reliable urinary breakpoint for Augmentin susceptibility using disk diffusion.
- To evaluate the accuracy of these methods in classifying bacterial susceptibility and resistance.
Main Methods:
- Disk diffusion susceptibility tests for Augmentin were conducted on 239 patient isolates.
- Tests were interpreted using Stoke's criteria, the ICS method, and a modified error minimization technique.
- Minimal inhibitory concentration (MIC) served as the reference, with ≤16 mg/L indicating likely therapeutic success in UTIs.
Main Results:
- Zone radii of inhibition showed a strong correlation with minimal inhibitory concentration (MIC).
- The error minimization technique successfully established a urinary breakpoint (Zs ≥ 6 mm radius), with only 1% false susceptibility.
- A significant false-resistant rate (14%) was observed, necessitating alternative testing conditions for accurate resistance detection.
Conclusions:
- The error minimization technique offers a viable method for establishing Augmentin susceptibility breakpoints in UTIs.
- Current disk diffusion methods may overestimate resistance, requiring adjustments for accurate false-resistant rate determination.
- An indeterminate zone category (4 < Z1 < 6 mm) is recommended for resistance rates exceeding 20%.
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