Rapid disc diffusion antibiotic susceptibility testing for Pseudomonas aeruginosa, Acinetobacter baumannii and...

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Diagnostic Technology

Background:

• Antibiotic susceptibility testing (AST) is crucial for guiding antimicrobial therapy.
• Current AST methods, like disc diffusion, often require 18-24 hours for results.
• Faster AST methods are needed to combat rising antimicrobial resistance.

Purpose of the Study:

• To evaluate the feasibility of rapid disc diffusion antibiotic susceptibility testing (rAST) for key Gram-negative and Gram-positive bacteria.
• To assess the early discrimination of resistant bacterial populations from wild-type (WT) populations.
• To determine the need for clinical breakpoint adaptations for accurate rAST interpretation.

Main Methods:

• Tested rAST with 6-8 hour incubation for Enterococcus faecalis, Enterococcus faecium, Pseudomonas aeruginosa, and Acinetobacter baumannii.
• Utilized the WASPLab automation system for incubation and imaging of disc diffusion plates.
• Defined WT and non-WT populations using epidemiological cut-offs.

Main Results:

• rAST achieved >90% readability for A. baumannii and enterococci at 6-8 hours.
• High categorical agreement (95.3-97.4%) was observed between 6-hour rAST and 18-hour AST for these species.
• Vancomycin-resistant E. faecium were clearly separated from WT at 6 hours.
• P. aeruginosa showed lower readability (68.9% at 8 hours) but good agreement (94.8%).

Conclusions:

• Rapid AST is feasible for A. baumannii and enterococci, enabling faster clinical decisions.
• Early discrimination of resistant strains is possible with rAST.
• Adaptation of clinical breakpoints and/or buffer zones is necessary for accurate rAST interpretation, especially for P. aeruginosa.