The EUCAST rapid disc diffusion method for antimicrobial susceptibility testing directly from positive blood culture...

Area of Science:

• Clinical microbiology
• Antimicrobial resistance
• Infectious diseases

Background:

• Rising antimicrobial resistance necessitates faster diagnostic methods.
• Bloodstream infections require prompt antimicrobial susceptibility testing (AST) for effective treatment.

Purpose of the Study:

• To develop and validate a standardized rapid antimicrobial susceptibility testing (RAST) method based on EUCAST disc diffusion.
• To provide susceptibility reports within 4-8 hours of a positive blood culture (BC).

Main Methods:

• Tested 332 clinical isolates of seven common sepsis pathogens directly from BC bottles.
• Evaluated RAST performance at 4, 6, and 8 hours incubation.
• Assessed the impact of different BC bottles and pre-analytical delays on results.

Main Results:

• Interpretable results were obtained for 75% of isolates at 4 hours, increasing to 84% at 8 hours.
• High categorical agreement with the reference method was observed.
• Low error rates for false susceptibility (0.2%) and false resistance (0.1-1.2%) were achieved.

Conclusions:

• The EUCAST RAST method offers reliable AST results within 4-8 hours for key bloodstream pathogens.
• An 'Area of Technical Uncertainty' was introduced to manage variability and minimize errors.