Detection of clinical Serratia marcescens isolates carrying bla KPC-2 in a hospital in China

Serratia marcescens is an opportunistic and nosocomial pathogen found in the intensive care unit (ICU), but its antimicrobial resistance (AMR) is rarely addressed. Here, we reported two bla KPC-2 - positive S. marcescens strains, SMBC31 and SMBC50, recovered from the ICU of a hospital in Zhengzhou, China. The minimum inhibitory concentration (MIC) was determined using the broth microdilution method, while S1-PFGE was employed to demonstrate plasmid size approximation. Complete genome sequences were obtained through Illumina NovaSeq 6000 and Oxford Nanopore Technologies. Both strains exhibit resistance to meropenem and harbor the bla KPC-2 and bla SRT-1 resistance genes. The plasmid pSMBC31-39K in strain SMBC31 and pSMBC50-107K in strain SMBC50 were identified as carrying the bla KPC-2 gene. Notably, both of these plasmids were successfully transferred to Escherichia coli strain J53. Phylogenetic analysis based on plasmid sequences revealed that pSMBC31-39K exhibited high homology with plasmids found in Aeromonas caviae , Citrobacter sp., and Pseudomonas aeruginosa , while pSMBC50-107K showed significant similarity to those of E. coli and Klebsiella pneumoniae . Notably, the coexistence of bla KPC-2 and bla SRT-1 was observed in all 94 KPC-2-producing S. marcescens strains by mining all genomes available under the GenBank database, which were mainly isolated from hospitalized patients. The emergence of multidrug-resistant S. marcescens poses significant challenges in treating clinical infections, highlighting the need for increased surveillance of this pathogen.