Transcriptomic Analysis of the Impact of the tet(X4) Gene on the Growth Characteristics and Antibiotic Resistance Phenotypes of Escherichia coli Isolated from Musk Deer.

Escherichia coli (E. coli) is a ubiquitous opportunistic pathogen in nature and serves as an important reservoir for antibiotic resistance genes. The tet(X4) gene is a key determinant mediating tigecycline resistance. Although its core resistance mechanism, encoding a flavin-dependent monooxygenase, has been elucidated, the broader impact of the tet(X4) gene on the secondary regulatory networks of E. coli remains not fully understood. In recent years, multiple studies have indicated that the tet(X4) gene participates in pathways contributing to resistance to other antibiotics by regulating the expression of various genes. In this study, E. coli tet(X4) gene deletion and complementation strains were constructed to investigate the mechanisms by which the tet(X4) gene influences the growth characteristics and antibiotic resistance of E. coli. The minimum inhibitory concentrations (MICs) of 24 different antibiotics, as well as the degradation capacities of tetracycline and tigecycline, were determined for the wild-type, deletion, and complementation strains. In addition, a four-week starvation stress experiment was performed under both the presence and absence of sub-inhibitory concentrations of tigecycline, during which the bacterial growth curves, survival rates, and MIC variations were analyzed. Transcriptomic sequencing of the wild-type, deletion, and complementation strains identified 531 differentially expressed genes associated with ABC transporter activity, drug metabolism, and bacterial two-component systems. These findings provide reliable evidence for elucidating the mechanism by which the tet(X4) gene affects E. coli resistance, offering valuable insights into the prevention and control of tigecycline-resistant E. coli infections.