Identification of a novel plasmid-mediated tigecycline resistance-related gene, tet(Y), in Acinetobacter baumannii

Objectives: To characterize a novel plasmid-mediated tigecycline resistance-related gene, tet(Y), in a clinical Acinetobacter baumannii isolate from China.

Methods: The tet(Y)-encoded tigecycline-resistant A. baumannii 2016GDAB1 was screened through antimicrobial susceptibility testing and WGS. The function of tet(Y) was verified by complementation of tet(Y). The plasmid transferability and stability were detected via plasmid conjugation and in vitro Bacterial passaging. The 3D structure of Tet(Y) was predicted and docked using tFold and AutoDock Vina.

Results: The tigecycline-resistant A. baumannii 2016GDAB1 was isolated from bronchoalveolar lavage fluid of a patient with hospital-acquired pneumonia. However, this strain did not harbour any common tigecycline resistance genes, determinants or mutations. 2016GDAB1 belongs to the non-epidemic clone ST355 (Oxford scheme), which has been mainly reported in Animals. The tet(Y) gene was located on a 72 156 bp plasmid and genomic environment analysis revealed that Tn5393 may play a role in tet(Y) transmission, whereas phylogenetic analysis indicated the origin of tet(Y) as from Aeromonas. Overexpression of tet(Y) resulted in a 2- to 4-fold increase in tigecycline MIC. Introduction of the tet(Y)-harbouring plasmid p2016GDAB1 via electroporation resulted in a 16-fold increase in tigecycline MIC but failed to transfer into the tigecycline-susceptible A. baumannii recipient via conjugation. Isolates carrying the tet(Y) gene were vulnerable to tigecycline pressure and exhibited decreased susceptibility to tigecycline. A tet(Y)-carrying plasmid was stably maintained in the host strains.

Conclusions: This study identified the tigecycline resistance-related gene tet(Y) in A. baumannii. This gene conferred an increased tigecycline MIC and the transposable element Tn5393 may play a role in its transmission across isolates.