Emergence of plasmid-mediated tigecycline resistance (X4) gene in isolated from wild animals in captivity.

Background: Over the past few decades, antimicrobial resistance (AMR) has emerged as a global health challenge in human and veterinary medicine. Research on AMR genes in captive wild animals has increased. However, the presence and molecular characteristics of (X)-carrying bacteria in these animals remain unknown.

Methods: Eighty-four samples were collected from captive wild animals. (X) variants were detected using polymerase chain reaction and the isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. All isolated strains were subjected to antimicrobial susceptibility testing and whole-genome sequencing. The virulence of an strain carrying enterotoxin genes was assessed using a larval model.

Results: We isolated two (X4)-positive strains and one (X4)-positive strain. Antimicrobial susceptibility tests revealed that all three (X4)-carrying bacteria were sensitive to the 13 tested antimicrobial agents, but exhibited resistance to tigecycline. Notably, one (X4)-carrying strain producing an enterotoxin had a toxic effect on larvae. Whole-genome sequencing analysis showed that the two (X4)-carrying strains had more than 95% similarity to (X4)-containing strains isolated from pigs and humans in China.

Conclusion: The genetic environment of (X4) closely resembled that of the plasmid described in previous studies. Our study identified (X4)-positive strains in wildlife and provided valuable epidemiological data for monitoring drug resistance. The identification of enterotoxin-producing strains also highlights the potential risks posed by virulence genes.