Comprehensive investigations reveal high occurrence of tet(X) in blaNDM-positive Acinetobacter spp. from Chinese cattle production systems.

Livestock are recognized as critical reservoirs for carbapenem-resistant bacteria (CRB), yet systematic investigations into cattle production systems remain limited. Here, we sampled cattle, humans, flies, sludge, and beef from 14 cattle farms and 3 associated slaughterhouses. Results revealed a low prevalence (3.44%) of blaNDM-positive strains (n = 27) at the farm level across seven provinces in China in 2023, with 66.67% (18/27) of strains collected from two adjacent provinces, Henan and Shandong, in central and eastern China. All blaNDM-positive strains were isolated from cattle farms, in which 88.89% (24/27) were identified as Acinetobacter, including A. indicus, A. pseudolwoffii, and A. gandensis. Notably, 62.5% (15/24) of the Acinetobacter co-carried blaNDM-tet(X), among which 93.33% (14/15) co-harbored these genes on plasmids. Conjugation assay revealed that the blaNDM-tet(X) carried by A. indicus could be co-transferred to recipients (E. coli or Salmonella) across bacterial genera via the plasmid typed to rep_481. Phylogenetic analyses revealed that high genetic similarity (PFGE band similarity ≥85% and SNPs ≤10) is present among the strains isolated from the same farm, suggesting farm-level spread of blaNDM-positive strains. Genome analyses identified an atypical genetic context for the blaNDM-tet(X): ISAba125-blaNDM-bleMBL-trpF-TAT-IS1008-tet(X)-res-ISVsa3-XerD-IS1008. Compared with other livestock production systems, blaNDM in cattle has a lower prevalence and is typically carried by Acinetobacter rather than Enterobacteriaceae. Co-existence and co-transfer of blaNDM-tet(X) could accelerate the spread of carbapenem and tigecycline resistance among food-producing animals, posing a potential public health risk. Thus, further investigation and ongoing monitoring are required.