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

Simple SummaryEscherichia coli(E. coli) is an opportunistic pathogen and an important reservoir of antibiotic resistance genes. Thetet(X4) gene mediates tigecycline resistance by encoding a flavin-dependent monooxygenase. However, the mechanism by which this gene influences bacterial antibiotic resistance through regulating the expression of other genes is complex and not yet fully understood. In this study,E. coli tet(X4) deletion and complemented strains were constructed to explore the effects of this gene on bacterial growth and antibiotic resistance. We measured the minimum inhibitory concentrations (MICs) of 24 antibiotics and the degradation capability for tetracycline/tigecycline in the wild type, deletion, and complemented strains, and conducted a 4-week starvation stress experiment (with/without subinhibitory concentrations of tigecycline) to analyze growth curves, survival rates, and changes in MICs. Transcriptome sequencing identified 531 differentially expressed genes, which are associated with ABC transporter activity, drug metabolism, and two-component systems. These findings provide reliable insights into the mechanism by which thetet(X4) gene affectsE. coliantibiotic resistance and offer a reference for the prevention and control of tigecycline-resistantE. coliinfections.Escherichia coli(E. coli) is a ubiquitous opportunistic pathogen in nature and serves as an important reservoir for antibiotic resistance genes. Thetet(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 thetet(X4) gene on the secondary regulatory networks ofE. coliremains not fully understood. In recent years, multiple studies have indicated that thetet(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 thetet(X4) gene influences the growth characteristics and antibiotic resistance ofE. 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 thetet(X4) gene affectsE. coliresistance, offering valuable insights into the prevention and control of tigecycline-resistantE. coliinfections.