Multicenter study of automated systems for colistin susceptibility testing

Area of Science:

• Clinical microbiology
• Antimicrobial resistance surveillance
• Infectious diseases

Background:

• Broth microdilution (BMD) is the gold standard for colistin antimicrobial susceptibility testing (AST).
• Automated AST systems are widely used in clinical laboratories.
• Accurate colistin AST is crucial for patient management and monitoring resistance.

Purpose of the Study:

• Evaluate automated systems (BD Phoenix, Vitek2, MicroScan) for colistin AST in Enterobacterales.
• Compare automated system performance against BMD reference method.
• Assess suitability of automated systems as alternatives to BMD.

Main Methods:

• Multicenter study involving 8 laboratories using routine automated AST systems.
• Tested 20 colistin-resistant (COL-R) and 10 colistin-susceptible (COL-S) Enterobacterales isolates.
• Included reference strains tested in triplicate; results compared to BMD.

Main Results:

• BD Phoenix and MicroScan demonstrated accurate and reproducible categorical results for colistin AST.
• Vitek2 system exhibited suboptimal performance in detecting COL-R isolates.
• Vitek2 showed lower categorical agreement (88%) and precision (81%) for COL-R isolates near the breakpoint.

Conclusions:

• BD Phoenix and MicroScan are reliable automated alternatives for colistin AST in Enterobacterales.
• Vitek2 requires further optimization for accurate colistin susceptibility testing, especially for borderline MICs.
• Standardized automated AST methods are essential for effective antimicrobial stewardship.