Evaluation of Automated Disk Diffusion Antimicrobial Susceptibility Testing Using Radian® In-Line Carousel

Area of Science:

• Clinical microbiology
• Medical diagnostics
• Automation in healthcare

Background:

• Manual disk diffusion for antimicrobial susceptibility testing (AST) is accurate but labor-intensive and prone to interpretation errors.
• The Radian® In-Line Carousel automates pre-analytical steps and interpretation of disk diffusion AST.
• No prior evaluations of the Radian® system against manual disk diffusion methods existed.

Purpose of the Study:

• To evaluate the performance of the Radian® In-Line Carousel for automated disk diffusion AST.
• To assess the categorical agreement (CA) between the Radian® system and standardized manual disk diffusion.
• To investigate the thermostability of antibiotic disks within the Radian® carousel.

Main Methods:

• Standardized disk diffusion was used as the reference method.
• The Radian® In-Line Carousel was evaluated using EUCAST 2021 breakpoints.
• 135 non-duplicate bacterial strains from various sources were tested, including Enterobacterales, Enterococcus spp., P. aeruginosa, Staphylococcus spp., and Streptococcus spp.
• Antibiotic disk thermostability was assessed by testing strains over 7 days.

Main Results:

• Overall categorical agreement (CA) was high across all bacterial groups tested (95.3% to 98.0%).
• Very major error rates were ≤5% for all tested antibiotics.
• Antibiotic disks demonstrated thermostability for up to 4 days in the Radian® carousel.

Conclusions:

• The Radian® In-Line Carousel offers a fully automated, accurate solution for disk diffusion AST.
• This automation reduces workload, enhances standardization, and improves traceability in AST.
• The system ensures the stability of antibiotic disks, supporting reliable testing over several days.