Quality assurance of antimicrobial susceptibility testing by disc diffusion

Area of Science:

• Microbiology
• Clinical Diagnostics
• Pharmaceutical Sciences

Background:

• Antimicrobial susceptibility testing (AST) by diffusion methods is vital for guiding patient treatment.
• Ensuring the accuracy and reliability of AST results is paramount for effective antimicrobial stewardship.
• Quality assurance (QA) processes are indispensable for maintaining the integrity of diffusion-based AST.

Purpose of the Study:

• To highlight the importance of quality assurance in antimicrobial susceptibility testing using diffusion methods.
• To detail the components and benefits of internal and external quality assessment schemes.
• To emphasize the role of education in preventing and resolving errors in AST.

Main Methods:

• Routine internal quality control (IQC) using standardized control strains with defined zone size ranges.
• Application of statistical approaches to identify deviations from acceptable performance in IQC.
• Participation in external quality assessment (EQA) schemes for independent performance evaluation.
• Internal quality assessment (IQA) involving blinded retesting of routine samples.

Main Results:

• IQC facilitates continuous monitoring of test performance, detecting deviations from acceptable ranges.
• Unacceptable control test results necessitate investigation into potential sources of error (e.g., media, discs, inoculum, reading).
• EQA provides an independent performance assessment, while IQA complements EQA by detecting issues missed by other methods.

Conclusions:

• A comprehensive QA program, integrating IQC, EQA, IQA, and education, is essential for reliable antimicrobial susceptibility testing.
• Understanding potential error sources and atypical results enhances the ability to recognize, resolve, and prevent errors.
• Continuous education on AST limitations and methodologies improves the overall quality and accuracy of laboratory diagnostics.