Why This Matters:
- Clinical microbiology laboratories are increasingly adopting total laboratory automation (TLA) to improve standardization and throughput in antimicrobial susceptibility testing (AST).
- Disk diffusion remains a widely used AST method, but manual preparation of bacterial suspensions and plate streaking is labor-intensive and subject to variability.
- Validating automated tools such as Colibri® and WASP® is essential for ensuring accuracy, reducing hands-on time, and improving traceability in routine susceptibility workflows.
Automated bacterial suspension preparation with Colibri® combined with plate streaking by WASP® demonstrates high categorical agreement with manual methods for antibiotic disk diffusion susceptibility testing, supporting its use in total laboratory automation.
Key Findings:
Vanstokstraeten et al. (2025) validated the combination of Colibri® for automated bacterial suspension preparation and WASP® for plate streaking within the WASPLab® system for antibiotic disk diffusion testing.1 The study, performed in a clinical microbiology lab, included 201 non-duplicate clinical bacterial strains representing both Gram-positive (78) and Gram-negative (123) species with a range of resistance mechanisms.
- High overall categorical agreement: The automated method achieved 96.3% categorical agreement with the manual reference method (2186/2269 results), indicating strong concordance.
- Low error rates: Initial minor errors were observed in 2.7% of comparisons, major errors in 1.6%, and very major errors in 0.4%. After retesting discrepant isolates, major and very major error rates were reduced to 0.4% and 0% respectively. Discrepancies were conceptually attributed, in part, to more confluent growth observed when using the candidate method or potential heteroresistance.
- No issues were observed with specific species or colony morphologies, including mucoid, swarming, adherent, or small/friable colonies, indicating that the automated workflow handled all the phenotypes successfully.
- Discrepancy resolution confirms reliability: Repeat testing of isolates with initial discrepancies often reconciled differences and confirmed agreement, suggesting minor procedural variation rather than systematic bias.
- Broad organism coverage: The automated workflow performed effectively across diverse bacterial species and resistance phenotypes, demonstrating robustness across routine clinical isolates.
- Standardization potential: Automated preparation and streaking resulted in consistent plating and often more confluent growth, which may reduce variability compared to manual techniques.
Bigger Picture:
This validation study supports the use of Colibri® and WASP® within automated laboratory workflows to prepare bacterial suspensions and inoculate plates for antibiotic disk diffusion testing with performance comparable to manual methods. High categorical agreement and low error rates suggest that these automated tools can reduce hands-on time, improve repeatability, and strengthen standardization within AST processes. As clinical microbiology continues to embrace automation, validated automated workflows such as this can enhance operational efficiency and reliability. Future work should continue to evaluate these systems across broader organism sets and incorporate gold-standard reference methods like broth microdilution to further refine performance benchmarks.
(Image Credit: iStock/ 10174593_258)
References:
- Vanstokstraeten et al. (2025). Validation of Automated Bacterial Suspension Preparation by Colibri® and Plate Streaking by WASP® for Antibiotic Disk Diffusion Susceptibility Testing. Antibiotics.
