In vitro Synergistic and Bactericidal Effects of Aztreonam in Combination with Ceftazidime/ Avibactam, Meropenem/Vaborbactam and Imipenem/Relebactam Against Dual-Carbapenemase-Producing Enterobacterales

Ying Fu,1,2 Yufeng Zhu,1,3 Feng Zhao,1,2,4 Bingyan Yao,1,2 Yunsong Yu,5 Jun Zhang,1,2 Qiong Chen6 1Department of Clinical Laboratory, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, People’s Republic of China; 2Key Laboratory of Precision Medicine in Diagnosis and Monitoring Research of Zhejiang Province, Sir Run Run Shaw Hospital, Hangzhou, Zhejiang Province, People’s Republic of China; 3Department of Clinical Laboratory, Hangzhou Xixi Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, People’s Republic of China; 4Department of Clinical Laboratory, Zhejiang University Sir Run Run Shaw Alar Hospital, Alar, Xinjiang province, People’s Republic of China; 5Department of Infectious Diseases, Zhejiang Provincial People’s Hospital, Hangzhou, Zhejiang Province, People’s Republic of China; 6Department of Clinical Laboratory, Affiliated Hangzhou First People’s Hospital, School of Medicine, Westlake University, Hangzhou, Zhejiang Province, People’s Republic of ChinaCorrespondence: Qiong Chen; Jun Zhang, Email [email protected]; [email protected]: Our aim was to elucidate the resistance mechanisms and assess the combined synergistic and bactericidal activities of aztreonam in combination with ceftazidime/avibactam (CZA), meropenem/vaborbactam (MEV), and imipenem/relebactam (IMR) against Enterobacterales strains producing dual carbapenemases.Methods: Species identification, antimicrobial susceptibility testing and determination of carbapenemase type were performed for these strains. Plasmid sizes, plasmid conjugation abilities and the localization of carbapenemase genes were investigated. Whole-genome sequencing was performed for all strains and their molecular characteristics were analyzed. In vitro synergistic and bactericidal activities of the combination of aztreonam with CZA, MEV and IMR against these strains were determined using checkerboard assay and time-kill curve assay.Results: A total of 12 Enterobacterales strains producing dual-carbapenemases were collected, including nine K. pneumoniae, two P. rettgeri, and one E. hormaechei. The most common dual-carbapenemase gene pattern observed was bla(KPC-2+NDM-5) (n=4), followed by blaKPC-2+IMP-26 (n=3), bla(KPC-2+NDM-1) (n=2), bla(KPC-2+IMP-4) (n=1), bla(NDM-1+IMP-4) (n=1) and bla(KPC-2+KPC-2) (n=1). In each strain, the carbapenemase genes were found to be located on two distinct plasmids which were capable of conjugating from the original strain to the receipt strain E. coli J53. The results of the checkerboard synergy analysis consistently revealed good synergistic effects of the combination of ATM with CZA, MEV and IMR. Except for one strain, all strains exhibited significant synergistic activity and bactericidal activity between 2 and 8 hours.Conclusion: Dual-carbapenemase-producing Enterobacterales posed a significant threat to clinical anti-infection treatment. However, the combination of ATM with innovative β-lactam/β-lactamase inhibitor compounds had proven to be an effective treatment option.Keywords: dual-carbapenemase-producing enterobacterales, β‑lactam/β‑lactamase inhibitor combinations, aztreonam, checkerboard assay, time-kill curve