Characterisation of a Novel Tigecycline Resistance Gene tet (X22) and its Coexistence with bla NDM-1 in a Pseudomonas caeni Isolate

Objectives: The emergence of pathogens that are resistant to both tigecycline and carbapenem poses a threat to public health globally. Continuous emergence of novel tet (X) variants accelerates the tigecycline resistance crisis. This study aimed to characterise the novel tigecycline resistance gene tet (X22) and its coexistence with carbapenem resistance gene bla NDM-1 in Pseudomonas caeni. Methods: This P. caeni isolate co-harbouring tet (X22) and bla NDM-1 was systematically investigated using antimicrobial susceptibility testing, conjugation assays, genome sequencing, bioinformatic analyses, cloning of tet (X22) and functional analysis, and protein structure prediction. Results: The carbapenem-resistant and tigecycline-resistant P. caeni isolate CE14 was obtained from chicken faeces in 2022. CE14 carried multiple antibiotic resistance genes, including the novel tet (X22) and bla NDM-1 . Tet(X22) exhibited 64.72-90.48% amino acid identity with other variants [Tet(X) to Tet(X21)]. Cloning of the gene tet (X22) and protein structure prediction revealed that Tet(X22) confers resistance to tetracyclines, including tigecycline. tet (X22) and bla NDM-1 were located in two multidrug-resistant regions of the chromosome. Conclusions: The occurrence of the novel IS CR2 -flanked tet (X22) in P. caeni suggests that the tet (X) variant has adapted to new hosts and may widely spread to further expand the host range. The future global spread of such pathogens co-harbouring tet (X) and bla NDM variants needs to be continuously monitored according to the One Health approach. (c) 2023 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.

Automated summary

This study characterized a novel tigecycline resistance gene tet(X22) and its coexistence with carbapenem resistance gene blaNDM-1 in Pseudomonas caeni. The study found that tet(X22) confers resistance to tigecycline and may widely spread to different hosts. Continuous monitoring of the global spread of pathogens harboring tet(X) and blaNDM variants is necessary according to the One Health approach.