Bovine-Derived Acinetobacter indicus Co-Harboring Chromosomal tet(X3) and Plasmid-Located tet(X4) Isolated from Henan, China

The coexistence of antibiotic resistance genes (ARGs), particularly those conferring resistance to last-resort antibiotics, is increasingly present in lesser-studied bacterial species. Tigecycline is currently one of the last important barriers in the treatment of carbapenem-resistant bacterial infections, whose resistance gene, <i>tet</i>(X), is prevalent across multiple bacterial genera, but the coexistence of <i>tet</i>(X3) and <i>tet</i>(X4) in <i>Acinetobacter</i> sp. is rarely observed. Here, we report a strain co-harborin<i>g</i> the chromosomal <i>tet</i>(X3) and plasmid-borne <i>tet</i>(X4) isolated from a commercial beef cattle farm in Henan province, China. The strain exhibited resistance to ampicillin, gentamicin, chloramphenicol, sulfamethoxazole, tetracycline, doxycycline, tigecycline, and omadacycline. Based on whole-genome sequencing (WGS), the strain was identified as <i>A. indicus</i> using Average Nucleotide Identity (ANI) and digital DNA-DNA hybridization (dDDH). Chromosomal <i>tet</i>(X3) was identified in the genetic context, IS<i>Vsa3</i>-<i>XerD</i>-<i>tet</i>(X3)-<i>res</i>-IS<i>Vsa3</i>. The plasmid-located <i>tet</i>(X4) with the genetic context, IS<i>Vsa3</i>-<i>abh</i>-<i>tet</i>(X4)-IS<i>Vsa3</i>, and 14 additional resistance genes were located in multiple p<i>dif</i> modules. Two different typing methods, the Rep-based strategy (designed for <i>A. baumanii</i>) and MOB-typer, identified the <i>tet</i>(X4)-positive plasmid as GR31 and rep_cluster_1656, respectively. Conjugation assay failed to observe the transfer of the <i>tet</i>(X4)-positive plasmid into recipients, <i>E. coli</i> J53 and <i>Salmonella</i> LGJ2. The co-occurrence of <i>tet</i>(X3) and <i>tet</i>(X4) in <i>Acinetobacter</i> may suggest a risk of rapid dissemination of tigecycline resistance and the hidden presence of numerous undetected bacteria co-carrying high-risk ARGs in the agroecological system, both of which should cause particular concern.