Direct disk diffusion test using European Clinical Antimicrobial Susceptibility Testing breakpoints provides reliable...

Area of Science:

• Clinical microbiology
• Infectious diseases
• Antimicrobial resistance

Background:

• Sepsis necessitates prompt antibacterial treatment to minimize patient morbidity.
• Rapid preliminary results from positive blood cultures are crucial for timely intervention.
• Direct antimicrobial susceptibility testing (AST) offers a faster alternative to conventional methods.

Purpose of the Study:

• To evaluate the reliability of direct agar diffusion testing for AST.
• To compare direct AST results with VITEK2-based definitive AST using current EUCAST breakpoints.
• To assess the utility of direct AST in optimizing empiric antibiotic therapy.

Main Methods:

• Analysis of 428 isolates from routine blood cultures and 110 challenge strains.
• Performed direct agar diffusion-based AST and standard VITEK2-based AST.
• Evaluated 2803 bacterium-drug combinations against current EUCAST breakpoints.

Main Results:

• Achieved 95.47% clinical category agreement between direct AST and VITEK2.
• Reported 1.28% very major errors and 3.42% combined major/minor errors.
• Identified specific species-drug combinations with notable very major errors (e.g., Enterococcus spp.-gentamicin, Staphylococcus spp.-rifampicin).

Conclusions:

• Direct agar diffusion testing using EUCAST breakpoints accurately predicts definitive AST results for most combinations.
• The method demonstrates potential for optimizing empiric antibiotic therapy in sepsis management.
• Further evaluation is needed for specific challenging species-drug combinations.