Evaluating the impact of rapid antimicrobial susceptibility testing for bloodstream infections: a review of actionability, antibiotic use and patient outcome metrics

Multicenter evaluation of the eQUANT system for use with disk diffusion AST of gram-negative bacteria directly from positive blood cultures

Bloodstream infections frequently cause sepsis, a condition that can lead to organ dysfunction and death. Rapid antimicrobial susceptibility testing (AST) results are critical for appropriate medical intervention and to either de-escalate or escalate antibiotics to appropriate therapy. We describe the results from a multicenter clinical study evaluating the performance of the eQUANT system (Avails Medical, Inc., Menlo Park, CA). The eQUANT system generates a 0.5 McFarland equivalent suspension, the eMcFarland, directly from a positive blood culture bottle for use with downstream disk diffusion AST, thereby saving up to 24 hours compared to traditional AST workflow. A combination of fresh, prospectively collected clinical (42) and contrived (525) blood cultures were tested, and results for disk diffusion using the Avails eQUANT eMcFarland suspension as the inoculum were compared to disk diffusion results the next day using the standard 0.5 McFarland suspension prepared from plate subculture. Thirteen species of gram-negative rods were evaluated against 12 antibiotics. From the 2,679 pairs of AST results, overall categorical agreement was 95.0%. Overall very major errors, major errors, and minor errors were 0.15%, 0.60%, and 4.48%, respectively. The Avails eQUANT system has the potential to significantly accelerate the standard of care by eliminating the need for subculture.IMPORTANCERapid reporting of antimicrobial susceptibility test results for bacterial isolates from blood cultures is critical for timely implementation of optimal antimicrobial therapy and improves outcomes of sepsis patients. In this study, we demonstrate the accuracy and performance characteristics of the eQUANT system, which generates a 0.5 McFarland equivalent suspension, the eMcFarland, directly from a positive blood culture bottle for use with downstream disk diffusion antimicrobial susceptibility testing (AST). Using the eMcFarland suspension allows for accurate and standardized reporting of disk diffusion AST results from positive blood cultures.

Comparative Assessment of Rapid Identification and Antimicrobial Susceptibility Testing Methods for Bloodstream Infections in a Non-24/7 Clinical Microbiology Laboratory

Rapid identification and antimicrobial susceptibility testing are essential for timely bloodstream infection (BSI) management. This study aimed to investigate the performance and turnaround time of multiple rapid diagnostic methods in a microbiology laboratory without 24/7 operation. This study included 236 positive blood culture bottles. Rapid identification methods were assessed with the SepsiTyper kit and the FilmArray blood culture identification 2 (BCID2) panel. Rapid antimicrobial susceptibility testing (AST) methods involved direct AST using the BD Phoenix M50 system and QuantaMatrix direct and rapid antimicrobial susceptibility testing (dRAST) and resistance gene detection with the FilmArray BCID2 panel. Conventional methods were used to compare results. The turnaround time was analyzed from blood culture positivity to preparation initiation and from preparation initiation to result reporting. Both rapid identification methods significantly reduced the turnaround time (~1 day and 19 h) compared to conventional identification. SepsiTyper demonstrated higher species-level accuracy in monomicrobial samples, whereas BCID2 outperformed in polymicrobial cases. Among the rapid AST methods, BCID2 and dRAST enabled result reporting within 24 h of positivity. Preparation delays were >45% of the overall turnaround time. Rapid diagnostics substantially shortened the BSI diagnostic time, even in limited-operation settings. Their clinical utility may be improved through 24/7 laboratory workflows.

An Evaluation of the ASTar Automated Antimicrobial Testing System for Gram-Negative Bacteria in Positive Blood Cultures

Background: Prompt administration of optimal antibiotic therapy is essential in the management of bacteraemia to reduce morbidity and mortality and to facilitate antibiotic stewardship. To identify the most effective therapy, rapid and accurate antimicrobial susceptibility testing (AST) is essential. ASTar is an automated AST system that delivers minimum inhibitory concentrations (MICs) for 23 antimicrobials and is designed for testing Gram-negative bacteria directly from positive blood cultures, with results available after 6 h. Methods: The ASTar system was evaluated with 64 positive blood cultures from patients with bacteraemia and 56 simulated blood cultures inoculated with a range of antibiotic-resistant isolates. The ASTar results for 12 antibiotics commonly used in our hospitals were compared with the results derived from three different methods of disc susceptibility testing and MICs determined by broth microdilution (BMD). Results: For 121 isolates of Gram-negative bacteria, ASTar showed an average essential agreement of 87.2% and an average categorical agreement of 94%, when compared with BMD. Very major errors (false susceptibility) and major errors (false resistance) were associated with 0.9% and 3.4% of results, respectively. The results were at least as accurate as those obtained from EUCAST disc susceptibility methods (both rapid and overnight methods). Conclusions: The ASTar system is an effective method for delivering accurate and rapid (6 h) AST results for Gram-negative bacteria by the direct testing of positive blood cultures.