Molecular Mechanisms and Epidemiology of Carbapenem-Resistant Enterobacter cloacae Complex Isolated from Chinese Patients During 2004–2018

Shixing Liu,1 Na Huang,1 Cui Zhou,1 Yishuai Lin,2 Ying Zhang,2 Lingbo Wang,1 Xiangkuo Zheng,1 Tieli Zhou,1 Zhongyong Wang1 1Department of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, People’s Republic of China; 2School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang Province, People’s Republic of ChinaCorrespondence: Zhongyong Wang; Tieli ZhouDepartment of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, People’s Republic of ChinaTel +86-577-5557-9725; +86-577-8668-9885Email wangforever2000@163.com; wyztli@163.comBackground: The emergence and spread of carbapenem-resistant Enterobacter cloacae complex (ECC) have posed a serious threat to human health worldwide. This study aimed to investigate the molecular mechanism of carbapenem resistance and its prevalence among ECC in China.Methods: A total of 1314 ECC clinical isolates were collected from the First Affiliated Hospital of Wenzhou Medical University from 2004 to 2018. Sensitivity to antibiotics was determined using the agar dilution method. The production of carbapenemases and the prevalence of resistance-associated genes were investigated using PCR. The expression of outer membrane porin (OMP) genes (ompC/ompF) and cephalosporinase gene ampC was analyzed by quantitative real-time PCR. The effect of efflux pump mechanism on carbapenem resistance was tested. ECC was typed by multilocus sequence typing (MLST).Results: In this study, 113 carbapenem-nonsusceptible ECC strains were identified. The prevalence rates of carbapenemase genes blaKPC-2 and blaNDM were 12.4% (14/113) and 17.7% (20/113), and that of the extended-spectrum β-lactamase (ESBL) genes blaCTX-M, blaTEM, and blaSHV were 28.3% (32/113), 27.4% (31/113), and 14.2% (16/113), respectively. Among 67 carbapenem-nonsusceptible ECC isolates producing non-carbapenemase, low expression of ompC/ompF and overexpression of ampC were found in 46 and 40 strains, respectively. In addition, the carbapenem resistance was related to the overexpression of the efflux pump in the study. Finally, the 113 carbapenem-nonsusceptible ECC strains were categorized into 39 different sequence types using MLST.Conclusion: Carbapenem-nonsusceptible ECC strains producing non-carbapenemase were predominant. The low expression of OMP with the overexpression of cephalosporinase or production of ESBLs and overexpression of efflux pump might contribute to the resistance to carbapenem for carbapenem-nonsusceptible ECC strains producing non-carbapenemase. The blaNDM and blaKPC comprised the principal resistance mechanism of carbapenemase-producing ECC in the hospital, causing a threat to public health. Therefore, monitoring programs to prevent the emergence and further spread of antibiotic resistance are urgently needed.Keywords: carbapenemase, carbapenem-resistant mechanism, Enterobacter cloacae complex, epidemiology, non-carbapenemas