State Key Laboratory for Animal Disease Control and Prevention, Guangdong Laboratory for Lingnan Modern Agriculture, College of Veterinary Medicine, South China Agricultural University, Guangzhou, China.
Key Laboratory of Zoonosis of Ministry of Agricultural and Rural Affairs, National Risk Assessment Laboratory for Antimicrobial Resistant of Microorganisms in Animals, Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, Guangzhou, Guangdong, China.
mBio. 2024 May 8;15(5):e0021824. doi: 10.1128/mbio.00218-24. Epub 2024 Apr 2.
Antibiotic resistance could rapidly emerge from acquiring the mobile antibiotic resistance genes, which are commonly evolved from an intrinsic gene. The emergence of the plasmid-borne mobilized efflux pump gene cluster renders the last-resort antibiotic tigecycline ineffective, although its evolutionary mechanism remains unclear. In this study, we investigate the regulatory mechanisms of the progenitor NfxB-MexCD-OprJ, a chromosomally encoded operon that does not mediate antibiotic resistance in the wild-type version, and its homologs, TNfxB1-TMexCD1-TOprJ1 mediating high-level tigecycline resistance, and TNfxB3-TMexCD3-TOprJ1. Mechanistic studies demonstrated that in , MexCD expression was under a weaker promoter, P and inhibited by a strong repressor NfxB. For , TMexCD1 was highly expressed owing to the presence of a strong promoter, P, and an inactive suppressor, TNfxB1, with a T39R mutation that rendered it unable to bind to promoter DNA. In , TMexCD3 expression was intermediate because of the local regulator TNfxB3, which binds to two inverted repeat sequences of P. Additionally, TNfxB3 exhibited lower protein expression and weaker DNA binding affinity than its ancestor NfxB, together with their promoter activities difference explaining the different expression levels of homologs. Distinct fitness burdens on these homologs-carrying bacteria were observed due to the corresponding expression level, which might be associated with their global prevalence. In summary, our data depict the mechanisms underlying the evolution and dissemination of an important mobile antibiotic resistance gene from an intrinsic chromosomal gene.IMPORTANCEAs antibiotic resistance seriously challenges global health, tigecycline is one of the few effective drugs in the pipeline against infections caused by multidrug-resistant pathogens. Our previous work identified a novel tigecycline resistance efflux pump gene cluster in animals and humans, together with its various variants, a rising clinical concern. Herein, this study focused on how the local regulation modes of evolved to a highly expressed efflux pump. Through comparative analysis between three homologs and their progenitor , modes, we demonstrated the evolutionary dynamics from a chromosomal silent gene to an active state. We found the de-repression of the local regulator and an increase of the promoter activity work together to promote a high production of drug efflux machines and enhance multidrug resistance. Our findings revealed that TMexCD1-TOprJ1 adopts a distinct evolutionary path to achieve higher multidrug resistance, urgently needing tight surveillance.
抗生素耐药性可以通过获得移动抗生素耐药基因迅速出现，这些基因通常是从内在基因进化而来的。质粒携带的可移动外排泵基因簇的出现使最后一线抗生素替加环素无效，尽管其进化机制尚不清楚。在这项研究中，我们研究了染色体编码操纵子 NfxB-MexCD-OprJ 的调节机制，该操纵子在野生型中不介导抗生素耐药性，以及其同源物 TNfxB1-TMexCD1-TOprJ1 介导高水平替加环素耐药性和 TNfxB3-TMexCD3-TOprJ1。机制研究表明，在 中，MexCD 的表达受到较弱启动子 P 的控制，并受到强抑制剂 NfxB 的抑制。对于 ，TMexCD1 由于存在强启动子 P 和无活性抑制剂 TNfxB1 而高表达，TNfxB1 发生 T39R 突变，使其无法与启动子 DNA 结合。在 中，由于局部调节剂 TNfxB3 与 P 的两个反向重复序列结合，TMexCD3 的表达处于中间水平。此外，TNfxB3 的蛋白表达和 DNA 结合亲和力均低于其前身 NfxB，其启动子活性差异解释了 同源物的不同表达水平。由于相应的表达水平，观察到这些携带同源物的细菌存在明显的适应性负担，这可能与它们的全球流行率有关。总之，我们的数据描绘了从内在染色体基因进化和传播重要的移动抗生素耐药基因的机制。
重要性：
由于抗生素耐药性严重威胁着全球健康，替加环素是对抗多药耐药病原体感染的少数有效药物之一。我们之前的工作在动物和人类中发现了一种新型替加环素耐药外排泵基因簇 ，以及其各种变体，这是一个日益引起关注的临床问题。在此，本研究重点关注 如何从染色体沉默基因进化为高表达的外排泵。通过对三个 同源物及其前体 之间的比较分析，我们证明了从染色体沉默基因到活跃状态的进化动态。我们发现，局部调节剂的去阻遏和启动子活性的增加共同促进了药物外排机器的高产量，并增强了多药耐药性。我们的研究结果表明，TMexCD1-TOprJ1 采用了一种独特的进化途径来实现更高的多药耐药性，迫切需要严密监测。
