Data_Sheet_1_Negative Impact of Citral on Susceptibility of Pseudomonas aeruginosa to Antibiotics.PDF

Essential oils (EOs) or their components are widely used by inhalation or nebulization to fight mild respiratory bacterial infections. However, their interaction with antibiotics is poorly known. In this study we evaluated the effects of citral, the main component of lemongrass oil, on in vitro susceptibility of Pseudomonas aeruginosa to antibiotics. Exposure of strain PA14 to subinhibitory concentrations of citral increased expression of operons encoding the multidrug efflux systems MexEF-OprN and MexXY/OprM, and bacterial resistance to anti-pseudomonal antibiotics including imipenem (twofold), gentamicin (eightfold), tobramycin (eightfold), ciprofloxacin (twofold), and colistin (≥128-fold). Use of pump deletion mutants showed that in addition to efflux other mechanisms were involved in this citral-induced phenotype. Determination of Zeta potential suggested that citral impairs the cell surface binding of aminoglycosides and colistin used at low concentrations (≤10 μg/mL). Moreover, experiments based on Raman spectroscopy and high-resolution mass spectrometry demonstrated formation of a Schiff base between the aldehyde group of citral and amino-groups of tobramycin and colistin. Chemical synthesis of tobracitryl, the imine compound resulting from condensation of citral and tobramycin, confirmed the loss of antibiotic activity due to adduct formation. Altogether these data point to the potential risk concern of self-medication with EOs containing citral in patients suffering from P. aeruginosa chronic lung infections and being treated with aerosols of aminoglycoside or colistin.

精油（Essential Oils, EOs）及其组分常通过吸入或雾化方式，用于对抗轻度呼吸道细菌感染。然而，其与抗生素的相互作用机制目前仍鲜为人知。本研究以柠檬草油的主要组分柠檬醛为研究对象，评估其对铜绿假单胞菌（Pseudomonas aeruginosa）体外抗生素敏感性的影响。将PA14菌株暴露于柠檬醛的亚抑菌浓度环境中，可上调编码多药外排系统MexEF-OprN与MexXY/OprM的操纵子表达水平，并使细菌对多种抗假单胞菌抗生素的耐药性提升：亚胺培南（2倍）、庆大霉素（8倍）、妥布霉素（8倍）、环丙沙星（2倍）以及粘菌素（≥128倍）。通过外排泵缺失突变体实验证实，除多药外排系统外，柠檬醛诱导的该表型还涉及其他作用机制。Zeta电位检测结果显示，当氨基糖苷类与粘菌素以低浓度（≤10 μg/mL）使用时，柠檬醛会削弱二者与细菌细胞表面的结合能力。此外，基于拉曼光谱与高分辨质谱的实验证实，柠檬醛的醛基可与妥布霉素、粘菌素的氨基基团结合形成希夫碱（Schiff base）。通过化学合成柠檬醛-妥布霉素亚胺（tobracitryl，即柠檬醛与妥布霉素缩合得到的亚胺类化合物），证实了加合物的形成会导致抗生素活性丧失。综上，本研究数据提示：对于患有铜绿假单胞菌慢性肺部感染且正在接受氨基糖苷类或粘菌素雾化治疗的患者，自行使用含柠檬醛的精油可能存在潜在风险。