Direct β-lactam inactivation method: A new low-cost assay for the rapid detection of carbapenemase- or extended-spectrum-β-lactamase-producing Enterobacterales directly from positive blood culture bottles

ABSTRACT

We validate and evaluate a new phenotypic assay, named direct β-lactam inactivation method (dBLIM), for the rapid and simultaneous detection of carbapenemase or extended-spectrum-cephalosporinase activity directly from Enterobacterales (EB) positive blood cultures (BCs). It originates from the carbapenem inactivation method (CIM), an inexpensive and highly sensitive assay for carbapenemase activity detection.

dBLIM cut off values to detect ESBL and carbapenemase activity resulted ≤ 12mm for 5 μg cefotaxime disk and for 10 μg meropemen disk, respectively.

dBLIM assessment was performed on both aerobic and anaerobic BC bottles spiked with 422 characterized EB strains, classifiable into the following 4 phenotypic groups: 1) extended-spectrum-β-lactamases (ESBLs)/AmpC-type-β-lactamases (ACBLs)/carbapenemases-non-producing (np-ESBL/ACBL/CARB) EB (n = 116); 2) ESBL-producing EB (n = 111); 3) AmpC-β-lactamase-producing EB (n=33); and 4) carbapenemase-producing EB (n = 162).

No false positive results were obtained in any of the np-ESBL/ACBL/CARB EB, ESBL and AmpC groups, demonstrating an overall assay specificity of 100%. There were no significant discrepancies in dBLIM performance between aerobic and anaerobic BCs across all groups, with the exception of VIM-expressing EB. Interestingly, among BCs spiked with bla_VIM-harboring EB, the sensitivity rate of the assay in anaerobic vs. aerobic bottles was 53.6% and 100%, respectively. In contrast, dBLIM performance was deemed excellent for the KPC, OXA-48, and NDM producers regardless of the type of bottle being tested, with a sensitivity rate ranging between 99% and 100%. Concerning the detection of the extended-spectrum-cephalosporinases, ESBL and AmpC-type, dBLIM sensitivity was 100% and 84-87%, respectively.

dBLIM could be a cost-effective and highly robust phenotypic screening method for the reliable detection of carbapenemases or extended-spectrum-cephalosporinases directly from BCs on the same day of bottle positivity detection.