Development of a national EUCAST challenge panel for antimicrobial susceptibility testing

Area of Science:

• Clinical microbiology
• Antimicrobial resistance surveillance
• Diagnostic test validation

Background:

• Clinical laboratories require reliable methods to test bacterial susceptibility to antibiotics.
• Validating antimicrobial susceptibility testing (AST) systems against established breakpoints is crucial for accurate patient treatment.
• The European Committee on Antimicrobial Susceptibility Testing (EUCAST) provides standardized breakpoints for antimicrobial susceptibility testing.

Purpose of the Study:

• To establish a challenge panel of bacterial strains for validating automated AST systems and disc diffusion methods against EUCAST breakpoints.
• To assess the performance of various AST systems and manufacturers using the developed challenge panel.
• To ensure the accuracy and reliability of antimicrobial susceptibility testing in clinical laboratories.

Main Methods:

• Selection of 117 bacterial strains based on resistance patterns from reference centers and clinical samples.
• Analysis of strains using three automated AST systems (Vitek, Phoenix, Microscan) and disc diffusion methods from five manufacturers.
• Application of selection criteria for categorical agreement and error rates (very major, major, minor) to establish the final challenge panel.

Main Results:

• Initial analysis of 117 strains revealed high error rates (43% with very major/major errors for at least two antibiotics), leading to exclusion.
• Only 10% of strains showed 100% categorical agreement across all antibiotics and systems.
• A final panel of 28 strains (14 Gram-positive, 14 Gram-negative) was selected, covering diverse resistance mechanisms. Pilot testing in 20 labs confirmed panel utility.

Conclusions:

• The developed 28-strain challenge panel effectively validates antimicrobial susceptibility testing (AST) systems against EUCAST breakpoints.
• The panel aids in identifying and minimizing errors in AST, enhancing diagnostic accuracy.
• Implementation of this panel will facilitate the consistent use of EUCAST breakpoints in clinical laboratories.