Antimicrobial resistance (AMR), especially the simultaneous resistance to several antibiotics (multidrug resistance [MDR]), is one of the greatest threats to global public health in the 21st century. Among animals, chickens, pigs, and cattle are reservoirs of these pathogens worldwide.

The emergence and dissemination of carbapenem-resistant Enterobacteriaceae (CRE) is a growing concern to animal and public health. However, little is known about the spread of CRE in food and livestock and its potential transmission to humans. To identify CRE strains from different origins and sources, 53 isolates were cultured from 760 samples including retail meat products, patients, and porcine excrement. Antimicrobial susceptibility testing was carried out, followed by phylogenetic typing, whole-genome sequencing, broth mating assays, and plasmids analyses. Forty-three Escherichia coli, nine Klebsiella pneumoniae, and one Enterobacter cloacae isolates were identified, each exhibiting multidrug-resistant phenotypes. Genetically, the main sequence types (STs) of E. coli were ST156 (n = 7), ST354 (n = 7), and ST48 (n = 7), and the dominant ST of K. pneumoniae is ST11 (n = 5). bla_NDM–5 (n = 40) of E. coli and bla_KPC–2 (n = 5) were the key genes that conferred carbapenem resistance phenotypes in these CRE strains. Additionally, the mcr-1 gene was identified in 17 bla_NDM-producing isolates. The bla_NDM–5 gene from eight strains could be transferred to the recipients via conjugation assays. Two mcr-1 genes in the E. coli isolates could be co-transferred along with the bla_NDM–5 genes. IncF and IncX3 plasmids have been found to be predominantly associated with bla_NDM gene in these strains. Strains isolated in our study from different sources and regions tend to be concordant and overlap. CRE strains from retail meat products are a reservoir for transition of CRE strains between animals and humans. These data also provide evidence of the dissemination of CRE strains and carbapenem-resistant genes between animal and human sources.

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.