Evaluation of the BL-RED test and comparison with the β-LACTA test for rapid detection of resistance to third-generation cephalosporins in <i>Enterobacterales</i> on early culture of positive blood cultures

The dissemination of multidrug-resistant <i>Enterobacterales</i>, particularly those resistant to third-generation cephalosporins (3GC), poses a significant public health challenge. This study evaluated the performance of the Beta-Lactamase Rapid Electrochemical Detection (BL-RED) test (CORIS BioConcept, Belgium) alongside the β-LACTA test (Bio-Rad, France), another routinely used technique in our laboratory, for the rapid detection of 3GC-resistant <i>Enterobacterales</i> from 4 h subcultures of positive blood cultures. A total of 178 isolates were included: 55 clinical isolates with characterized resistance mechanism and 123 isolates from positive blood cultures prospectively collected between April and July 2023. Parallel testing with the BL-RED and β-LACTA tests was performed, and the results were compared to those of conventional antibiotic susceptibility testing by disk diffusion, following the 2024 EUCAST recommendations. The sensitivity, the specificity, the observed positive predictive value, and the observed negative predictive value for 3GC resistance detection in the prospective cohort were 74%, 100%, 100%, and 95%, respectively, for both the BL-RED and β-LACTA tests. Both tests demonstrated good performance in detecting 3GC-resistant <i>Enterobacterales</i>, particularly those expressing common Ambler class A beta-lactamases. However, they were less effective in detecting 3GC resistance due to the presence of other Ambler class families, notably overproduced chromosomal and plasmid-mediated Ambler class C beta-lactamases. The ease of use of these tests makes them suitable for routine microbiology laboratory testing. We propose a diagnostic algorithm combining the use of either the BL-RED and β-LACTA tests with that of MALDI-TOF MS in order to initiate targeted antibiotic therapy early.IMPORTANCEAntimicrobial resistance, especially among <i>Enterobacterales</i> resistant to third-generation cephalosporins (3GC), represents a major public health threat. Delayed detection of these resistant pathogens can lead to inappropriate empirical antibiotic therapy, with risk of treatment failures and further spread of resistance. This study underscores the value of rapid diagnostic tools, specifically the BL-RED and β-LACTA tests, for the rapid identification of 3GC-resistant <i>Enterobacterales</i> directly from positive blood cultures. By enabling quicker therapeutic decision-making, these assays provide a practical solution for microbiology laboratories to enhance patient management and contribute to global efforts in mitigating the impact of antibiotic-resistant infections.