Lichens are known to be useful and important in ethanopharmacology since ages and still possess substantial interest in alternative medical practices around the world. The intent of this investigation was to evaluate and to understand the antibacterial potential of usnic acid which was isolated from Himalyan fruticose lichen Ramalina roesleri. Usnic acid is predicted for its pharmaceutical properties through in -silico studies. Binding efficiency of usnic acid with Penicillin binding protein-PBP2a, a protein which is responsible for conferring resistance in Staphylococcus aureus was accessed using in-silico interaction assays comparing with oxacillin and ceftaroline. Further, the validation of in-silico modelling was checked by determining the antibacterial potential of usnic acid against methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates. In total, 28 clinical isolates collected from hospitals/medical students were included in the study and the anti-Staphylococcal activity was determined using agar plate dilution method followed by time-kill kinetics and synergistic studies. The scanning electron microscopic (SEM) pictures were obtained to show the cell wall disruption of MRSA by usnic acid.

Docking results clearly indicated the enhanced binding potential of usnic acid (Glide XP G Score: 10.968; Glide energy −64.869) with PBP2a which is better than the energy range of reference compound, oxacillin (Glide XP G Score: 6.596; Glide energy −53.285) and roughly comparable to the co-crystallized ligand ceftaroline (Glide XP G Score: 12.20; Glide energy −70.322). Cefteroline is known to be more active against MRSA compared to oxacillin. The minimum inhibitory concentrations (MICs) of usnic acid against the clinical isolates of MRSA and reference strain (NCTC-6571) were in the range of 32–128 μg/ml. The high affinity of usnic acid to bind with PBP2a which is demonstrated via in-silico studies is further confirmed by the impressive inhibitory activity of usnic acid on MRSA clinical isolates.

众所周知，地衣自古以来就在乙醇药理学中有用且重要，并且仍然对世界各地的替代医学实践具有浓厚的兴趣。这项调查的目的是评估和了解从喜马拉雅果糖地衣Ramalina roesleri中分离出的松萝酸的抗菌潜力。通过计算机研究预测松萝酸的药学特性。松萝酸与青霉素结合蛋白-PBP2a 的结合效率，PBP2a 是一种负责赋予金黄色葡萄球菌抗性的蛋白质，与苯唑西林和头孢洛林相比，使用计算机内相互作用测定法获得。此外，在计算机上的验证通过确定松萝酸对耐甲氧西林金黄色葡萄球菌(MRSA) 临床分离株的抗菌潜力来检查模型。总共从医院/医学生收集的 28 种临床分离株被纳入研究，并使用琼脂平板稀释法确定抗葡萄球菌活性，然后进行时间杀伤动力学和协同研究。获得的扫描电子显微镜 (SEM) 图片显示松萝酸对 MRSA 的细胞壁破坏。

对接结果清楚地表明松萝酸（Glide XP G 得分：10.968；Glide 能量 -64.869）与 PBP2a 的结合潜力增强，优于参考化合物苯唑西林的能量范围（Glide XP G 得分：6.596；Glide 能量 -53.285） ) 并且与共结晶配体头孢洛林大致相当（Glide XP G 分数：12.20；Glide 能量 -70.322）。与苯唑西林相比，头孢特罗林对 MRSA 的活性更高。松萝酸对临床分离株 MRSA 和参考菌株 (NCTC-6571) 的最低抑菌浓度 (MIC) 在 32-128 μg/ml 范围内。松萝酸与 PBP2a 结合的高亲和力通过计算机研究证明，松萝酸对 MRSA 临床分离株的显着抑制活性进一步证实了这一点。