Laboratory evaluation of a rapid, automatic susceptibility testing system: report of a collaborative study

Area of Science:

• Clinical Microbiology
• Antimicrobial Susceptibility Testing
• Laboratory Diagnostics

Background:

• Accurate antimicrobial susceptibility testing (AST) is crucial for guiding effective antibiotic therapy.
• Standardized methods like the Bauer-Kirby disk diffusion and agar dilution are benchmarks for AST.
• Evaluating novel automated systems is essential for improving laboratory efficiency and diagnostic accuracy.

Purpose of the Study:

• To assess the performance of the Autobac 1 system in antimicrobial susceptibility testing.
• To compare the Autobac 1 system against the Bauer-Kirby disk diffusion method.
• To evaluate both methods against the agar dilution technique as a reference standard.

Main Methods:

• A collaborative study involving seven laboratories.
• Comparison of Autobac 1 results with Bauer-Kirby disk diffusion.
• Comparison of both methods against the International Collaborative Study agar dilution technique.
• Assessment of interpretive agreement across 17 antimicrobial agents.
• Evaluation of method reproducibility.

Main Results:

• Autobac 1 demonstrated 91.5% overall interpretive agreement with the disk diffusion method across 17 antimicrobial agents.
• Agreement between Autobac 1 and disk diffusion was ≥90% for 13 agents.
• Both Autobac 1 and disk diffusion showed high and equivalent agreement (approx. 90%) with the agar dilution reference method.
• Discrepancies often involved susceptible results on Autobac 1 versus intermediate/resistant results on other methods, potentially due to Autobac 1's narrow interpretive zone.
• Interpretive reproducibility was similar between Autobac 1 and disk diffusion methods.

Conclusions:

• The Autobac 1 system exhibits a high level of agreement with the standardized disk diffusion method for antimicrobial susceptibility testing.
• Autobac 1 performance is comparable to disk diffusion when validated against the agar dilution reference method.
• The Autobac 1 system is a reliable alternative for routine antimicrobial susceptibility testing, though careful interpretation is needed for specific drug-organism combinations.