Qian Xu,1 Ying Fu,2 Feng Zhao,2 Yan Jiang,1 Yunsong Yu1 1Department of Infectious Diseases, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Key Laboratory of Microbial Technology and Bioinformatics of Zhejiang Province, Hangzhou City, Zhejiang Province, 310016, People’s Republic of China; 2Clinical Laboratory, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou City, Zhejiang Province 310016, People’s Republic of ChinaCorrespondence: Yan Jiang; Yunsong Yu Tel/Fax +86-571-8600-6142Email jiangy@zju.edu.cn; yvys119@zju.edu.cnIntroduction: Although carbapenem-resistant Enterobacteriaceae (CRE) have been thoroughly investigated as the pathogens most commonly associated with clinical infections, data on Serratia marcescens are inadequate and superficial.Methods: In this study, we characterized 36 carbapenem-resistant Serratia marcescens (CRSM) isolates in our hospital from April 2018 to March 2019 by analysing whole-genome sequencing (WGS) data. The molecular typing of the isolates was performed using both pulsed-field gel electrophoresis (PFGE) and core genome multilocus sequence typing (cgMLST).Results: Thirty-three of the 36 isolates showed carbapenem resistance conferred by a blaKPC-2-harbouring plasmid, while the remaining three isolates were characterized by overexpression of beta-lactamase combined with porin loss. The blaKPC-2 genes in all the isolates were located on a plasmid of ∼ 103 kb, except one, which was on a plasmid of ∼ 94 kb. The gene structure surrounding blaKPC-2 in the plasmids was confirmed by integration of a partial Tn4401 structure and an intact IS26 as previously reported. Most of the plasmids also contained a mobile genetic element (MGE) comprising qnr and ISKpn19, which provided evidence of horizontal transfer of antibiotic resistance genes.Conclusion: The thirty-six CRSM isolates were mainly clonally disseminated with a blaKPC-2-harbouring plasmid in our hospital. The gene structure surrounding blaKPC-2 as an MGE, as well as the qnr segment, might be acquired by horizontal gene transfer, and it could aggravate the infection and increase the difficulty of clinical treatment.Keywords: Serratia marcescens, carbapenem resistance, blaKPC-2-harbouring plasmid
