Due to excessive use of antimicrobial agents in the treatment of infectious diseases, bacteria have developed resistance to antibacterial drugs and toxic compounds. The development of multidrug efflux pumps is one of the important mechanisms of bacterial drug resistance. A multidrug efflux pump, EmrD, belonging to the major facilitator superfamily of transporters, confers resistance to many antimicrobial agents. BasSR, a typical two-component signal transduction system (TCS), regulates susceptibility to the cationic antimicrobial peptide, polymyxin B, and the anionic bile detergent, deoxycholic acid, in Escherichia coli. However, whether or not the BasSR TCS affects susceptibility or resistance to other antimicrobial agents and transcription of emrD has not been reported in E. coli. In the present study, we constructed the basSR mutants of wild-type MG1655 and clinical strain APECX40 and performed antimicrobial susceptibility testing, antibacterial activity assays, real-time reverse transcription–PCR experiments and electrophoretic mobility shift assays (EMSA) to investigate the molecular mechanism by which BasSR regulates the EmrD multidrug efflux pump. Results showed that the basSR mutation increased cell susceptibility to eight antimicrobial agents, including ciprofloxacin, norfloxacin, doxycycline, tetracycline, clindamycin, lincomycin, erythromycin, and sodium dodecyl sulfate, by downregulating the transcriptional levels of emrD. Furthermore, EMSA indicated that BasR could directly bind to the emrD promoter. Therefore, this study was the first to demonstrate that BasSR activates transcription of emrD by binding directly to its promoter region, and then decreases susceptibility to various antimicrobial agents in E. coli strains, APECX40 and MG1655.

中文翻译：

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两组分系统BasSR在EmrD多药外排在大肠杆菌中表达的调控作用。

由于在治疗传染病中过量使用抗菌剂，细菌已发展出对抗菌药物和有毒化合物的抗性。多药外排泵的发展是细菌耐药性的重要机制之一。属于转运蛋白主要促进者超家族的多药外排泵EmrD赋予了对许多抗菌剂的抗性。BasSR是一种典型的两组分信号转导系统（TCS），可调节大肠杆菌中阳离子抗微生物肽多粘菌素B和阴离子胆汁清洁剂脱氧胆酸的敏感性。但是，BasSR TCS是否影响对其他抗菌剂的敏感性或耐药性，emrD的转录尚未见报道。大肠杆菌。在本研究中，我们构建了野生型MG1655和临床菌株APECX40的basSR突变体，并进行了抗生素敏感性测试，抗菌活性测定，实时逆转录PCR实验和电泳迁移率变动测定（EMSA），以研究分子机制。 BasSR借此调节EmrD多药外排泵。结果表明，basSR突变可通过下调emrD的转录水平来提高对八种抗菌剂的细胞敏感性，其中包括环丙沙星，诺氟沙星，强力霉素，四环素，克林霉素，林可霉素，红霉素和十二烷基硫酸钠。此外，EMSA指出BasR可以直接与emrD结合启动子。因此，这项研究首次证明BasSR通过直接结合其启动子区域激活emrD的转录，然后降低了大肠杆菌菌株APECX40和MG1655中对各种抗菌剂的敏感性。