Pilot study evaluation of the eQUANT™ system for accelerated antimicrobial susceptibility testing of gram-negative organisms directly from positive blood cultures

Abstract

We describe results from a multicenter pilot study evaluating the eQUANT^TM system for rapid generation of a standardized inoculum (0.5 McFarland equivalent) directly from blood cultures positive for target gram-negative bloodstream pathogens for same-day antimicrobial susceptibility testing (AST) by disk diffusion, MicroScan and Vitek2 methods. Out of 167 blood cultures that met study criteria (monomicrobial with one of 9 target gram-negative species), colony counts from eQUANT suspensions of 164 (98.2 %) were within the acceptable range of 1-2e8 ± 0.6 log₁₀ CFU/mL (2.51×10⁷ to 7.96×10⁸ CFU/mL). Average eQUANT testing time was 72 min and AST results were available an average of 22.3 h earlier compared to next day testing. Overall performance of direct versus next day AST was excellent, with categorical agreement of 97.5 %, 96.9 % and 96.7 %, respectively, by disk diffusion, MicroScan and Vitek methods. For clinical application this could facilitate antibiotic stewardship and provide targeted antibiotic therapy recommendations earlier.

Keywords: Blood culture; Potentiometric sensing of changes in oxidation-reduction potential; Rapid antimicrobial susceptibility testing; eQUANT.