Direct Ethylenediaminetetraaceticacid-Modified β-Lactam Inactivation Method: An Improved Method to Identify Serine-Carbapenemase-, Metallo-β-Lactamase-, and Extended-Spectrum-β-Lactamase-Producing Enterobacterales Directly from Positive Blood Culture

Rapid identification of extended-spectrum-β-lactamase (ESBL)-, serine carbapenemase-, and metallo-β-lactamase (MBL)-producing Enterobacterales directly from positive blood culture (BC) bottles is of paramount importance to early optimize antimicrobial management and infection control measures. In this study, we describe and evaluate an improved variant of direct β-lactam inactivation method, named direct ethylenediaminetetraaceticacid-modified-β-lactam inactivation method (deBLIM). The deBLIM test is designed to detect ESBL or carbapenemase activity and to differentiate serine-carbapenemases from MBLs directly from Enterobacterale-positive BCs. The deBLIM was evaluated on both aerobic and anaerobic BCs spiked with 167 characterized Enterobacterale isolates. The deBLIM showed 100% sensitivity in detecting KPC and OXA-48-like serine carbapenemase, CTX-M, SHV variants, and TEM-10 ESBLs both in aerobic and anaerobic conditions. In contrast, a significant discrepancy between aerobic and anaerobic BCs was observed in detecting MBLs. The sensitivity rate in aerobic BCs was of 100% for all metalloenzyme types, whereas only 56.1% and 80% of VIM and NDM producers were detected in anaerobic bottles, respectively. IMP-producing Escherichia coli NCTC 13476 was also not detected in the anaerobic BC. No false positive result was observed among ESBL producers and broad-spectrum-β-lactamase nonproducers, demonstrating an overall specificity of 100%. The deBLIM could be a cost-effective screening method for the identification of ESBLs, serine carbapenemases, and MBLs directly from Enterobacterale-positive BCs on the same day of bottle positivity detection. Nevertheless, it must be considered its poor performance in detecting MBLs in the anaerobic condition.