Gut microbes thrive by utilising host energy and, in return, provide valuable benefits, akin to a symbiotic relationship. Here, metagenomic sequencing was performed to characterise and compare the community composition, diversity and antibiotic resistance of the gut microbiota of Relict gull (Larus relictus) and Anatidae species. Alpha diversity analysis revealed that the intestinal microbial richness of L. relictus was significantly lower than that of Anatidae, with distinct differences observed in microbial composition. Notably, the intestines of L. relictus harboured more pathogenic bacteria such as clostridium, which may contribute to the decline in their population and endangered status. A total of 117 strains of Escherichia coli were isolated, with 90.60% exhibiting full susceptibility to 21 antibiotics, while 25.3% exhibited significant biofilm formation. Comprehensive Antibiotic Resistance Database data indicated that glycopeptide resistance genes were the most prevalent type carried by migratory birds, alongside quinolone, tetracycline and lincosamide resistance genes. The abundance of resistance genes carried by migratory birds decreased over time. This metagenomic analysis provides valuable insights into the intestinal microbial composition of these wild bird species, offering important guidance for their conservation efforts, particularly for L. relictus, and contributing to our understanding of pathogen spread and antibiotic-resistant bacteria.

The widespread application of carbapenems and other broad-spectrum antibiotics has significantly escalated the threat posed by highly drug-resistant Klebsiella pneumoniae to human public health. In this research, we isolated a carbapenem-resistant K. pneumoniae strain from the feces of pet dogs at a veterinary hospital in Changchun, Jilin Province, China. To gain insights into its genetic makeup and resistance mechanisms, we conducted comprehensive whole-genome sequencing and antimicrobial susceptibility testing on the isolated strain. Our findings revealed the presence of three distinct plasmids within the strain, classified as IncFIB&IncFII, IncR, and IncX3. Notably, the bla_NDM-5 gene, conferring resistance to carbapenems, was uniquely harbored on the IncX3 plasmid, which was devoid of any other resistance genes beyond bla_NDM-5. In contrast, the remaining two plasmids, IncFIB&IncFII and IncR, were found to encode an array of additional drug resistance genes, contributing to the strain’s broad-spectrum resistance phenotype. The IncX3 plasmid, specifically, measures 45,829 bp in length and harbors the IS5D-bla_NDM-5-Ble-MBL-PRAI cassette, which has been closely linked to the dissemination of bla_NDM-5 genes in K. pneumoniae strains. We reported the bla_NDM-5-carrying IncX3 in K. pneumoniae isolates recovered from the pet dog and revealed the molecular characterization. Emphasis should be placed on, and continuous monitoring carried out for, the dissemination of K. pneumoniae harboring the bla_NDM-5 gene among humans, companion animals, and their related environments.