Co-production of MCR-1 and NDM-5 in Escherichia coli isolated from a colonization case of inpatient Siyuan Feng,1,2,* Cong Shen,1,2,* Hongtao Chen,3 Xiaobin Zheng,4 Yong Xia,5 Lan-Lan Zhong,1,2 Xi Huang,6 Xinwei Wu,7 Guo-Bao Tian1,2 1Department of Immunology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China; 2Key Laboratory of Tropical Diseases Control, Sun Yat-sen University, Ministry of Education, Guangzhou, China; 3Department of Laboratory, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, China; 4Department of Respiratory Medicine, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, China; 5Department of Clinical Laboratory Medicine, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, China; 6Program of Pathobiology and Immunology, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, China; 7Department of Microbiology, Guangzhou Center for Disease Control and Prevention, Guangzhou, China *These authors contributed equally to this work Abstract: Colistin is increasingly used as an antibiotic of last resort for treating carbapenem-resistant Enterobacteriaceae. Mobile colistin resistance gene mcr-1 has been increasingly reported in Enterobacteriaceae around the world. Of particular concern is the spread of mcr-1 into carbapenemase-producing Enterobacteriaceae, which results in highly drug-resistant strains that are potentially untreatable. Notably, such mcr-1-carrying isolates harboring carbapenemase genes have been reported in animals and patients with infection. Here, we report an Escherichia coli strain carrying co-transferable mcr-1-harboring IncX4 and blaNDM-5-harboring IncX3 plasmids, which was recovered in the context of fecal colonization. Keywords: Escherichia coli, MCR-1, NDM-5, co-production