Molecular Characterization of Carbapenem-Resistant Serratia marcescens Clinical Isolates in a Tertiary Hospital in Hangzhou, China

INTRODUCTION: 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 bla(KPC-2)-harbouring plasmid, while the remaining three isolates were characterized by overexpression of beta-lactamase combined with porin loss. The bla(KPC-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 bla(KPC-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 bla(KPC-2)-harbouring plasmid in our hospital. The gene structure surrounding bla(KPC-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.