Table 2_Exogenous cystine increases susceptibility of drug-resistant Salmonella to gentamicin by promoting oxidation of glutathione metabolism and imbalance of intracellular redox levels.xlsx

IntroductionAntibiotic overuse has caused the development of bacterial resistance, which is a major threat to public health. Intracellular metabolic processes are essential for maintaining the normal physiological activities of bacteria, and an increasing body of research has demonstrated a significant association between metabolic alterations and the development of drug resistance. Numerous studies have demonstrated that the addition of adjuvants can counteract bacterial antibiotic resistance.
MethodCystine treatment was verified in vitro to promote the lethal effect of gentamicin on Salmonella using in vitro bactericidal counting methods. The metabolic differences in Salmonella enterica Typhimurium standard strain ATCC 14028 with or without the addition of cystine were analyzed via untargeted metabolomics. The multifunctional electronic enzyme marker was used to determine intracellular reduced glutathione/oxidized glutathione (GSH/GSSG), ferrous iron on (Fe2+), and reactive oxygen species (ROS) levels. The expression of glutathione and stress genes was determined using real-time quantitative PCR.
ResultWe confirmed that exogenous cystine increased the lethal effect of gentamicin against strain S. enterica Typhimurium (ATCC 14028) and other clinically resistant Salmonella serotypes. Exogenous cystine stimulated the metabolism of the cell and activated the glutathione pathway while altering the GSH/GSSG ratio, which placed bacteria in a state of redox imbalance with increased Fe2+ and ROS levels. Our results suggest that when bacterial redox levels are reprogrammed, bacterial susceptibility to antibiotics can also change.
DiscussionThis study confirms that cystine enhances the antimicrobial efficacy of gentamicin against drug-resistant Salmonella. Through the application of metabolomics, the underlying metabolic mechanisms by which cystine exerts its effects on Salmonella have been elucidated, offering a novel perspective in the domain of metabolic reprogramming aimed at counteracting drug resistance. Furthermore, these findings reinforce the potential role of small-molecule metabolites as effective adjuvants to enhance antibiotic action.

引言
抗生素滥用导致细菌耐药性的产生，这对公共健康构成重大威胁。细胞内代谢过程对维持细菌正常生理活动至关重要，越来越多的研究表明，代谢改变与耐药性的发展存在显著关联。多项研究证实，添加佐剂可对抗细菌的抗生素耐药性。

方法
本研究采用体外杀菌计数法，验证了胱氨酸处理可增强庆大霉素对沙门氏菌的杀伤作用。通过非靶向代谢组学（untargeted metabolomics）分析了添加与未添加胱氨酸的鼠伤寒沙门氏菌（Salmonella enterica Typhimurium）标准菌株ATCC 14028的代谢差异。使用多功能酶标仪检测了细胞内还原型谷胱甘肽/氧化型谷胱甘肽（GSH/GSSG）、亚铁离子（Fe²+）以及活性氧（ROS）水平。采用实时定量聚合酶链式反应（real-time quantitative PCR）检测了谷胱甘肽相关基因与应激基因的表达量。

结果
本研究证实，外源性胱氨酸可增强庆大霉素对鼠伤寒沙门氏菌ATCC 14028菌株以及其他临床耐药沙门氏菌血清型的杀伤作用。外源性胱氨酸可刺激细菌细胞代谢，激活谷胱甘肽通路，同时改变GSH/GSSG比值，使细菌处于氧化还原失衡状态，伴随Fe²+与ROS水平升高。本研究结果表明，当细菌的氧化还原水平被重编程时，其对抗生素的敏感性也会发生改变。

讨论
本研究证实，胱氨酸可增强庆大霉素对抗耐药沙门氏菌的抗菌活性。通过应用代谢组学技术，本研究阐明了胱氨酸作用于沙门氏菌的潜在代谢机制，为旨在对抗耐药性的代谢重编程领域提供了全新视角。此外，本研究结果进一步强化了小分子代谢物作为有效佐剂以增强抗生素药效的潜在作用。