SRA

SRA calibrates disk diffusion antibiotic susceptibility test results using Single-Strain Regression Analysis to correlate zone diameters with minimum inhibitory concentrations (MICs) and to derive species-specific zone breakpoints.

Key Features:

• Single-Strain Regression Analysis (SRA): Calculates regression lines and SRA constants (A and B) that correlate disk diffusion zone diameters with MICs for calibration of zone breakpoints.
• Customizable Disk Potency Calibration: Uses disks with varying antibiotic concentrations (for example, fusidic acid) to calibrate disk diffusion results according to disk potency and laboratory conditions.
• Species-Specific Interpretations: Determines zone breakpoints tailored to particular bacterial strains, exemplified by calibration for Clostridium difficile.
• Integration of Reference MIC Methods: Incorporates MIC values obtained by alternative methods such as the E-test as input for regression calibration.
• Interpretation Alignment with Pharmacological Limits: Applies pharmacological MIC limits (for example, those from the Swedish Reference Group for Antibiotics, SRGA) to align calibrated disk diffusion interpretations with standardized MIC criteria.

Scientific Applications:

• Antibiotic Susceptibility Testing (AST): Provides calibrated zone breakpoints to improve the precision of disk diffusion AST by translating zone diameters into MIC-based interpretations.
• Clinical Microbiology: Supports determination of bacterial susceptibility or resistance (e.g., to fusidic acid in C. difficile) to inform treatment decisions and antimicrobial stewardship.

Methodology:

Compute regression lines from paired zone diameter and MIC data to derive SRA constants A and B, then apply pharmacological MIC limits to the calibrated disk diffusion results to set interpretive zone breakpoints.