Chunhong Zou1,2 ,* Jie Wei3 ,* Baoju Shan4,5 ,* Xian Chen,6 Deqiang Wang,2,7 Siqiang Niu1 1Department of Laboratory Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 2College of Laboratory Medicine, Chongqing Medical University, Chongqing, People’s Republic of China; 3Department of Laboratory Medicine, West China Second University Hospital, Key Laboratory of Obstetric & Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education, Sichuan University, Chengdu, People’s Republic of China; 4Pediatric Research Institute; Ministry of Education Key Laboratory of Child Development and Disorders; National Clinical Research Center for Child Health and Disorders (Chongqing), China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Children’s Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 5Chongqing Key Laboratory of Pediatrics, Children’s Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 6Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China; 7The Key Laboratory of Molecular Biology of Infectious Diseases Designated by the Chinese Ministry of Education, Chongqing Medical University, Chongqing, People’s Republic of China*These authors contributed equally to this workCorrespondence: Siqiang NiuDepartment of Laboratory Medicine, The First Affiliated Hospital of Chongqing Medical University, No. 1 Youyi Road, Yuzhong District, Chongqing 400016, People’s Republic of ChinaTel +86-23-8901 2742Fax +86-23-8901 2513Email siqiangniu@cqmu.edu.cnPurpose: To assess the antimicrobial activities of ceftazidime/avibactam (CAZ/AVI) and aztreonam/avibactam (ATM/AVI) against carbapenem-resistant Enterobacteriaceae (CRE) isolates collected from three secondary hospitals in Southwest China between 2018 and 2019.Materials and Methods: A total of 120 unique CRE clinical isolates were collected and carbapenemase genes were detected using PCR. Antimicrobial susceptibility was determined using standard broth microdilution method and the results were interpreted according to CLSI breakpoints.Results: The 120 carbapenem-resistant strains included 92 Klebsiella pneumoniae, 10 Escherichia coli, 10 Enterobacter cloacae, five Klebsiella aerogenes, and three Klebsiella oxytoca isolates. Seventy-four percent of these 120 CRE isolates were collected from patients located in non-ICUs; 65.0% of these CRE isolates were collected from male patients; and 34.2% of these isolates were isolated from respiratory tracts. Four different carbapenemase genes were identified among 103 carbapenemase-producing Enterobacteriaceae (CPE) isolates, including blaKPC-2 (n=77), blaNDM-1 (n=16), blaNDM-5 (n=12) and blaIMP-4 (n=2). Overall, 21.7%, 37.5%, 40.8%, 75.0%, and 100% of the CRE strains were susceptible to levofloxacin, trimethoprim/sulfamethoxazole, amikacin, CAZ/AVI, and ATM/AVI, respectively. In addition, antimicrobial susceptibility testing showed that 96.7% isolates (n=116) were resistant to aztreonam, and the addition of avibactam (4 mg/L) significantly reduced the MICs of those aztreonam-resistant isolates by more than 128-fold (range: ≤ 0.125– 4 mg/L), and 90.0% (n=108) of total 120 isolates were inhibited at ATM/AVI concentration ≤ 1 mg/L.Conclusion: Our study revealed significant antimicrobial resistance among the CRE isolates against some commonly used antibiotics in three secondary Chinese hospitals. ATM/AVI exhibited potent activity against CRE isolates, including double carbapenemase-producing isolates, whereas CAZ/AVI was active against all KPC producers.Keywords: carbapenem-resistant Enterobacteriaceae, carbapenemase-producing Enterobacteriaceae, ceftazidime/avibactam, aztreonam/avibactam