Carbapenemase detection testing in the era of ceftazidime/avibactam-resistant KPC-producing Enterobacterales: A 2-year experience

Objectives: The aim of this study was to investigate the prevalence of ceftazidime/avibactam (CZA) resistance among carbapenemase-producing Enterobacterales (CPE) blood culture isolates as well as the performance of the main carbapenemase phenotypic detection methods to identify KPC variants associated with CZA resistance. Methods: Non-duplicate CPE strains isolated from blood cultures during 2018-2020 were tested for antimicrobial susceptibility. Molecular testing was used to identify carbapenemase-producers. Strains harbouring bla(KPC) and with a CZA minimum inhibitory concentration (MIC) >= 8 mg/L were investigated by sequencing. Subsequentially, five phenotypic carbapenemase detection methods were evaluated on these strains, namely the modified carbapenem inactivation method (mCIM), Rapidec (R) Carba NP, the disk diffusion synergy test, NG-Test CARBA (R) 5 and RESIST-5 O.O.K.N.V. Results: Overall, the CZA resistance rate was high (13.7%) and remained relevant (5.9%) excluding metallo-beta-lactamases-producers. All isolates harbouringbla(KPC) mutants (n = 8) were associated with reduced carbapenem MICs and negative results by all detection methods based on revelation of enzyme activity. Lateral flow immunoassays failed to detect KPC-31 (n = 4) and KPC-33 (n = 2) but correctly identified KPC-14 (n = 2). Conversely, isolates harbouring wild-type KPC genes (n = 3) were associated with high-level CZA resistance and carbapenem resistance and tested positive by all of the evaluated methods. Conclusion: In the era of CZA-based therapies, molecular bla(KPC) identification followed by a carbapenem hydrolysis-based phenotypic assay could be the most reasonable diagnostic algorithm to detect all KPC-producers and to identify mutants associated with impaired carbapenemase activity and CZA resistance. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.