Abstract

Staphylococcus aureus causes severe infections and among all methicillin-resistant S. aureus (MRSA) remains a great challenge in spite of decade research of antibacterial compounds. Even though some synthetic antibiotics have been developed, they are not effective against MRSA, and hence, there is a search for natural, alternative and plant-based antibacterial compound. In this connection, catechin isolated from cashew nut shell was investigated for its antibacterial potential against MRSA. Catechin exhibited zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) in a range of 15.1–19.5 mm and 78.1–156.2 μg/ml, respectively, against ATCC and clinical isolates of MRSA. Among all clinical isolates, clinical isolate-3 exhibited highest sensitivity to catechin. Catechin has arrested the growth of MRSA strains and also caused toxicity by membrane disruption which was illustrated by AO/EB fluorescence staining. Increased nucleic acid leakage (1.58–28.6-fold) and protein leakage (1.40–23.50-fold) was noticed in MRSA due to catechin treatment when compared to methicillin. Bacteria treated with catechin at its MIC showed 1.52-, 1.87- and 1.74-fold increase of ROS production in methicillin susceptible S. aureus (MSSA), MRSA and clinical isolate-3 strains, respectively, as compared to control. Superoxide dismutase (5.31–9.63 U/mg protein) and catalase (1573–3930 U/mg protein) were significantly decreased as compared to control in catechin-treated S. aureus. Thus, catechin exhibited antibacterial activity through oxidative stress by increased production of ROS and decreased antioxidant enzymes. Altogether results suggest that catechin is a promising lead compound with antibacterial potential against MRSA.

Key points

• Catechin was isolated and identified as active compound in cashew nut shell.

• Catechin exhibited antimicrobial activity against clinical isolates of MRSA.

• Bacterial cell wall damage was caused by catechin in MRSA strains.

• Catechin increased the oxidative stress in MRSA by intracellular ROS production.

中文翻译：

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从腰果壳中分离出的儿茶素通过ROS介导的氧化应激表现出对MRSA临床分离物的抗菌活性。

摘要

金黄色葡萄球菌引起严重感染，其中包括耐甲氧西林的金黄色葡萄球菌尽管对抗菌化合物进行了十年的研究，但（MRSA）仍然是一个巨大的挑战。即使已经开发了一些合成抗生素，它们对MRSA也无效，因此，人们正在寻找天然的，替代的和基于植物的抗菌化合物。因此，研究了从腰果壳中分离出的儿茶素具有抗MRSA的潜力。儿茶素对ATCC和MRSA临床分离株的抑制区（ZOI）和最小抑菌浓度（MIC）分别为15.1–19.5 mm和78.1–156.2μg/ ml。在所有临床分离株中，临床分离株3对儿茶素的敏感性最高。儿茶素阻止了MRSA菌株的生长，并通过膜破坏引起了毒性，这可以通过AO / EB荧光染色来说明。与甲氧西林相比，由于儿茶素治疗，MRSA中发现核酸泄漏（1.58–28.6倍）和蛋白质泄漏（1.40–23.50倍）增加。儿茶素在MIC处处理的细菌在易感甲氧西林的ROS产生中分别增加了1.52、1.87和1.74倍与对照相比，金黄色葡萄球菌（MSSA），MRSA和临床孤立3菌株。与儿茶素处理的金黄色葡萄球菌相比，超氧化物歧化酶（5.31–9.63 U / mg蛋白）和过氧化氢酶（1573–3930 U / mg蛋白）显着降低。因此，儿茶素通过增加ROS的产生和减少抗氧化酶的氧化应激表现出抗菌活性。总的结果表明，儿茶素是一种有前途的先导化合物，对MRSA具有抗菌潜力。

关键点

•儿茶素被分离并鉴定为腰果壳中的活性化合物。

•儿茶素对MRSA的临床分离株表现出抗菌活性。

•细菌细胞壁损伤是由MRSA菌株中的儿茶素引起的。

•儿茶素通过细胞内ROS的产生增加MRSA中的氧化应激。