Nowicki Dariusz, Krause Klaudyna, Szamborska Patrycja, Żukowska Adrianna, Cech Grzegorz M, Szalewska-Pałasz Agnieszka
Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdańsk, Gdańsk, Poland.
Front Microbiol. 2021 Jan 14;11:591802. doi: 10.3389/fmicb.2020.591802. eCollection 2020.
Bacterial resistance to known antibiotics comprises a serious threat to public health. Propagation of multidrug-resistant pathogenic strains is a reason for undertaking a search for new therapeutic strategies, based on newly developed chemical compounds and the agents present in nature. Moreover, antibiotic treatment of infections caused by enterotoxin toxin-bearing strain-enterohemorrhagic (EHEC) is considered hazardous and controversial due to the possibility of induction of bacteriophage-encoded toxin production by the antibiotic-mediated stress. The important source of potentially beneficial compounds are secondary plant metabolites, isothiocyanates (ITC), and phytoncides from the Brassicaceae family. We reported previously that sulforaphane and phenethyl isothiocyanate, already known for their chemopreventive and anticancer features, exhibit significant antibacterial effects against various pathogenic bacteria. The mechanism of their action is based on the induction of the stringent response and accumulation of its alarmones, the guanosine penta- and tetraphosphate. In this process, the amino acid starvation path is employed via the RelA protein, however, the precise mechanism of amino acid limitation in the presence of ITCs is yet unknown. In this work, we asked whether ITCs could act synergistically with each other to increase the antibacterial effect. A set of aliphatic ITCs, such as iberin, iberverin, alyssin, erucin, sulforaphen, erysolin, and cheirolin was tested in combination with sulforaphane against . Our experiments show that all tested ITCs exhibit strong antimicrobial effect individually, and this effect involves the stringent response caused by induction of the amino acid starvation. Interestingly, excess of specific amino acids reversed the antimicrobial effects of ITCs, where the common amino acid for all tested compounds was glycine. The synergistic action observed for iberin, iberverin, and alyssin also led to accumulation of (p)ppGpp, and the minimal inhibitory concentration necessary for the antibacterial effect was four- to eightfold lower than for individual ITCs. Moreover, the unique mode of ITC action is responsible for inhibition of prophage induction and toxin production, in addition to growth inhibition of EHEC strains. Thus, the antimicrobial effect of plant secondary metabolites by the stringent response induction could be employed in potential therapeutic strategies.
细菌对已知抗生素产生耐药性对公众健康构成了严重威胁。多重耐药病原菌的传播促使人们基于新开发的化合物和天然存在的物质寻找新的治疗策略。此外，由于抗生素介导的应激可能诱导噬菌体编码毒素的产生，因此对携带肠毒素的肠出血性大肠杆菌（EHEC）引起的感染进行抗生素治疗被认为是危险且有争议的。潜在有益化合物的重要来源是植物次生代谢产物、异硫氰酸酯（ITC）以及十字花科植物的植物杀菌素。我们之前报道过，已因其化学预防和抗癌特性而闻名的萝卜硫素和苯乙基异硫氰酸酯对多种病原菌具有显著的抗菌作用。它们的作用机制基于严格反应的诱导及其警报素（鸟苷五磷酸和四磷酸）的积累。在这个过程中，通过RelA蛋白利用了氨基酸饥饿途径，然而，在存在ITC的情况下氨基酸限制的确切机制尚不清楚。在这项工作中，我们研究了ITC是否可以相互协同作用以增强抗菌效果。一组脂肪族ITC，如异硫氰酸苄酯、异硫氰酸苄酯醇、异硫氰酸蒜素、异硫氰酸芥酸、萝卜硫素、异硫氰酸乙酯苯酯和异硫氰酸苯乙酯，与萝卜硫素联合用于测试对……的抗菌效果。我们的实验表明，所有测试的ITC单独都表现出很强的抗菌作用，但这种作用涉及由氨基酸饥饿诱导引起的严格反应。有趣的是，过量的特定氨基酸会逆转ITC的抗菌作用，所有测试化合物的共同氨基酸是甘氨酸。观察到异硫氰酸苄酯、异硫氰酸苄酯醇和异硫氰酸蒜素的协同作用也导致了（p）ppGpp的积累，并且抗菌效果所需的最低抑菌浓度比单个ITC低四到八倍。此外，ITC独特的作用方式除了抑制EHEC菌株的生长外，还负责抑制噬菌体诱导和毒素产生。因此，通过严格反应诱导产生的植物次生代谢产物的抗菌作用可用于潜在的治疗策略。
