The emergence of multi-drug resistant and virulence gene carrying Escherichia coli strains in the dairy environment: a rising threat to the environment, animal, and public health

The prevalent dynamic and genetic characterization of mcr-1 encoding multi-drug resistant Escherichia coli strains recovered from poultry in Hebei, China

OBJECTIVES

Colistin is known as the last resort antibiotic to treat the infections caused by multi-drug resistant (MDR) foodborne pathogens. The emergence and widespread dissemination of plasmid-mediated colistin resistance gene mcr-1 in the E. coli incurs potential threat to public health. Here, we investigated the epidemiology, transmission dynamics, and genetic characterization of mcr-1 harboring E. coli isolates from poultry origin in Hebei province, China.

METHODS

A total of 297 fecal samples were collected from the two large poultry farms in Hebei province, China. The samples were processed for E. coli identification by MALDI-TOF-MS and 16S rD4A sequencing. Then, mcr-1 gene harboring E. coli strains were identified by PCR and subjected to antimicrobial susceptibility testing by broth microdilution assay. The genomic characterization of the isolates was done by whole genome sequencing using the various bioinformatics tools, and multi-locus sequence typing (MLST) was done by sequence analysis of the seven housekeeping genes. The conjugation experiment was done to check the transferability of mcr-1 along with the plasmid stability testing.

RESULTS

A total of six mcr-1 E. coli isolates with MIC of 4 μg/mL were identified from 297 samples (2.02%). The mcr-1 harboring E. coli were identified as MDR and belonged to ST101 (n=4) and ST410 (n=2). The genetic environment of mcr-1 presented its position on IncHI2 plasmid in four isolates and p0111 in two isolates which is rarely reported plasmid type for mcr-1. Moreover, both type of plasmids was transferable to recipient J53, and mcr-1 was flanked by three mobile elements ISApl1, Tn3, and IS26 forming a novel backbone Tn3-IS26-mcr-1- pap2-ISApl1 on p0111 plasmid. The phylogenetic analysis shared a common lineage with mcr-1 harboring isolates from the environment, human and animals which indicate its horizontal spread among the diverse sources, species, and hosts.

CONCLUSION

This study recommends the one health approach for future surveillance across multiple sources and bacterial species to adopt relevant measures and reduce global resistance crises.

Tn3-like structures co-harboring of blaCTX-M-65, blaTEM-1 and blaOXA-10 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 blaCTX-M-65 gene and the role of its associated mobile genetic elements (MGEs) in the bovine-derived Escherichia coli. After PCR identification, two plasmids carrying blaCTX-M-65 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 blaCTX-M-65 was mapped using the Easyfig software. WGS analysis revealed Tn3-like composite transposons bearing blaCTX-M-65, blaTEM-1, and blaOXA-10 in the IncHI2-type plasmids of these two E. coli ST1508 strains. A phylogenetic tree was generated from all 48 assembled E. coli isolates blaCTX-M-65, blaTEM-1, and blaOXA-10 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 blaCTX-M-65 on Tn3-like composite transposons contributes to an increased risk of its transmission in E. coli derived from dairy cattle.