High altitude medicinal plants against multidrug resistant microorganisms: Screening and chemical profiling of the most active nepeta longibracteata

Abstract

Background and Objective: Development of resistance amongst microbes towards commonly used antibiotics is of major concern in recent years. Considering the growing attention for search of new antimicrobial agents, seven relatively unexplored high altitude plants were screened for antimicrobial property against multidrug resistant clinical isolates. Methodology: Solvent extraction followed by fractionation afforded 28 components. Antibacterial activity was evaluated against Gram-positive Staphylococcus aureus and three Gram-negative viz., Serratia sp., Acinetobacter sp. and E. coli clinical isolates. Antifungal activity was evaluated against Aspergillus niger, Fusarium moniliforme and Candida albicans. All experiments were carried out in triplicates and expressed as Mean±SD. Results: The n-hexane fraction of Nepeta longibracteata (NlH) and Rhodiola imbricata (RiH) exhibited most significant antibacterial activity against E. coli and S. aureus (MIC 125 µg mL-1), while antifungal activity was exhibited only by NlH with MIC 250 µg mL-1. Phytochemical profiling of NlH by GC-MS showed 14 compounds where n-hexadecanoic acid and methyl hexadecanoate constituted 67.7% of the total constituents. Scanning Electron Microscopy (SEM) was performed with NlH at MIC to study the morphological changes on E. coli cell membrane. This study revealed shortening and swelling of cells and multiple blisters formation on cell surface compared to untreated control. Conclusion: The results of the present study have identified NlH as the most potent fraction against multidrug resistant microorganisms. The membrane permeabilizing activity of NlH was also established through SEM analysis. These results may be exploited in future to increase the efficacy of conventional antibiotics by enhancing their cellular uptake. Such a strategy holds immense potential in the current scenario of continuous emergence of antibiotics resistant microorganisms.