In vitro activity of imipenem/relebactam, meropenem/vaborbactam, ceftazidime/avibactam, cefepime/zidebactam and other novel antibiotics against imipenem-non-susceptible Gram-negative bacilli from Taiwan.

Abstract

To investigate the susceptibility of imipenem-non-susceptible Escherichia coli (INS-EC), Klebsiella pneumoniae (INS-KP), Acinetobacter baumannii (INS-AB) and Pseudomonas aeruginosa (INS-PA) to novel antibiotics. MICs were determined using the broth microdilution method. Carbapenemase and ESBL phenotypic testing and PCR for genes encoding ESBLs, AmpCs and carbapenemases were performed. Zidebactam, avibactam and relebactam increased the respective susceptibility rates to cefepime, ceftazidime and imipenem of 17 INS-EC by 58.8%, 58.8% and 70.6%, of 163 INS-KP by 77.9%, 88.3% and 76.1% and of 81 INS-PA by 45.7%, 38.3% and 85.2%, respectively. Vaborbactam increased the meropenem susceptibility of INS-EC by 41.2% and of INS-KP by 54%. Combinations of β-lactams and novel β-lactamase inhibitors or β-lactam enhancers (BLI-BLE) were inactive against 136 INS-AB. In 58 INS-EC and INS-KP with exclusively blaKPC-like genes, zidebactam, avibactam, relebactam and vaborbactam increased the susceptibility of the partner β-lactams by 100%, 96.6%, 84.5% and 75.9%, respectively. In the presence of avibactam, ceftazidime was active in an additional 85% of 20 INS-EC and INS-KP with exclusively blaOXA-48-like genes while with zidebactam, cefepime was active in an additional 75%. INS-EC and INS-KP with MBL genes were susceptible only to cefepime/zidebactam. The β-lactam/BLI-BLE combinations were active against INS-EC and INS-KP without detectable carbapenemases. For INS-EC, INS-KP and INS-AB, tigecycline was more active than omadacycline and eravacycline but eravacycline had a lower MIC distribution. Lascufloxacin and delafloxacin were active in <35% of these INS isolates. β-Lactam/BLI-BLE combinations were active in a higher proportion of INS-EC, INS-KP and INS-PA. The susceptibility of novel fluoroquinolones and tetracyclines was not superior to that of old ones.