Genomic Insights into Plasmid Mediated Dissemination of blaKPC-2 and blaCTX-M-14 in a Fecal ST595 Serratia Marcescens Isolate

Yuyan Wang,1,* Huanran Zhang,2,* Yi Liu,3 Yifei Wang1 1Department of Emergency Medicine, Zhuji Traditional Chinese Medicine Hospital, Zhuji, People’s Republic of China; 2Department of Emergency Medicine, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, People’s Republic of China; 3Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yifei Wang, Email [email protected]: Serratia marcescens is an opportunistic pathogen with notable antimicrobial resistance features. The emergence of S. marcescens harboring the blaKPC-2 gene, which encodes a carbapenemase conferring resistance to carbapenems, poses a significant threat to public health. This study reports the detailed genomic characteristics of a blaKPC-2- and blaCTX-M-14-co-carrying S. marcescens strain L4843, isolated from a fecal sample.Methods: The isolate underwent antimicrobial susceptibility testing (AST) by broth microdilution. Whole-genome sequencing (WGS) was conducted using Illumina NovaSeq and Nanopore platforms. Unicycler was used for assembly and bioinformatics tools identified resistance genes, plasmid types, and mobile elements. Conjugation experiments with E. coli J53 as the recipient were carried out on MacConkey agar with sodium azide and imipenem. Transconjugants were confirmed by PCR amplification of resistance genes.Results: The genome of the S. marcescens isolate comprised 5,377,884 bp with a GC content of 59.8%. The blaKPC-2 gene, responsible for carbapenem resistance, was located on a repB(R1701) plasmid. The plasmid contains several copies of IS 26 and ISKpn19 elements, along with TnAs1 transposons. The isolate also harbored multiple resistance genes, including blaCTX-M-14, blaSRT-1, blaLAP-2, aac(3)-IId, and aac(6’)-Ic. The plasmid sequence was compared with other known sequences (CP047692, CP047686, MT269826), revealing significant homology. The alignment shows a conserved structure around blaKPC-2, indicating a shared dissemination mechanism for this resistance gene.Conclusion: The genomic characterization of a blaKPC-2- and blaCTX-M-14-co-carrying S. marcescens underscores the complexity and mobility of resistance mechanisms within this pathogen. To our knowledge, no published report has documented fecal S. marcescens carrying blaKPC-2 and blaCTX-M-14 in China to date, highlighting the surveillance value of our finding.Keywords: serratia marcescens, carbapenem-resistant, KPC-2, repB, R1701, plasmid, mobile genetic elements