Tn3-like structures co-harboring of bla, bla and bla in the plasmids of two Escherichia coli ST1508 strains originating from dairy cattle in China.

The purpose of this study was to determine the level of horizontal transmission of the bla gene and the role of its associated mobile genetic elements (MGEs) in the bovine-derived Escherichia coli. After PCR identification, two plasmids carrying bla were successfully transferred to the recipient E. coli J53 Azr through conjugation assays and subsequently selected for Whole-Genome sequencing (WGS) analysis. The resistance profiles of these two positive strains and their transconjugants were also determined through antimicrobial susceptibility tests. Whole genome data were acquired using both the PacBio sequencing platform and the Illumina data platform. The annotated results were then submitted to the Genbank database for accession number recording. For comparison, the genetic environment of plasmids carrying the resistance gene bla was mapped using the Easyfig software. WGS analysis revealed Tn3-like composite transposons bearing bla, bla, and bla in the IncHI2-type plasmids of these two E. coli ST1508 strains. A phylogenetic tree was generated from all 48 assembled E. coli isolates bla, bla, and bla from the NCBI Pathogen Detection database with our two isolates, showing the relationships and the contribution of SNPs to the diversity between genetic samples. This study suggests that the transmissibility of bla on Tn3-like composite transposons contributes to an increased risk of its transmission in E. coli derived from dairy cattle.