Implementing EUCAST rapid antimicrobial susceptibility testing method for sepsis: lessons learned in a tertiary care...

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Accurate and timely antimicrobial susceptibility testing (AST) is crucial for effective treatment of bloodstream infections.
• Traditional AST methods can delay targeted therapy, impacting patient outcomes.
• Evaluating novel, rapid AST methods is essential for improving clinical decision-making.

Purpose of the Study:

• To prospectively evaluate the EUCAST rapid AST methodology for direct susceptibility testing from positive blood culture bottles.
• To compare the performance of rapid AST against the CLSI disk-diffusion method for Gram-negative microorganisms.
• To assess the accuracy and reliability of rapid AST at different reading times (4, 6, and 8 hours).

Main Methods:

• Prospective evaluation of 80 Gram-negative isolates from blood cultures (E. coli, K. pneumoniae, P. aeruginosa, A. baumannii).
• Simultaneous processing using EUCAST rapid AST and CLSI disk-diffusion methods.
• Testing against a panel of key antibiotics including cefotaxime, ceftazidime, piperacillin-tazobactam, imipenem, meropenem, gentamicin, tobramycin, and trimethoprim-sulphamethoxazole.

Main Results:

• Overall categorical agreement for rapid AST reached 92.3% at the 8-hour reading time.
• Major Error rates decreased significantly to 1.7% at 8 hours, while Very Major Error rates were 3.3%.
• Results categorized as "Area of Technical Uncertainty" were significantly lower at 8 hours compared to 4 hours (5.2% vs 10.2%).

Conclusions:

• Rapid AST at 8 hours demonstrates equivalence to the CLSI disk-diffusion method, meeting most CLSI-M52 criteria for equivalence.
• Slightly higher Very Major Error rates were observed, necessitating careful interpretation.
• The study suggests reporting rapid AST results at a single 8-hour time point for clinical utility, despite challenges in resource-limited settings.