Antioxidant, antibacterial activity and in silico study of selected medicinal plants against pathogenic bacteria

Abstract

An increase in the number of antibiotic resistant bacteria worldwide has necessitated new antibacterial agents, mainly by medicinal plants. For this, the antioxidant and antibacterial activities of four Malaysian medicinal plants; Alpinia galanga, Centella asiatica, Clinacanthus nutans and Persicaria odorata extracts were evaluated against gram-positive (Bacillus subtilis, Staphylococcus epidermidis, Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA)) and gram-negative (Escherichia coli, Pseudomonas putida) in this study. The medicinal plants were extracted using solvents with different polarities and screened for the total phenolic contents via Folin-Ciocalteu method and antioxidant capacity by diphenyl-1-picrylhydrazyl (DPPH) activity. The antibacterial activities were conducted using disc diffusion, minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests. The most effective plant extract was further fractionated by column chromatography and thin layer chromatography. The fractions were then characterized using antibacterial assays, Zeta potential measurements, followed by scanning electron microscopic (SEM) observations and Gas Chromatography Mass Spectrometry (GCMS) analysis. Compounds identified were docked with Penicillin binding protein (PBP) using Autodock 4.0 and simulate (MD) by Gromacs 5.0.4. The findings from this study showed that acetone plant extracts exhibited the highest antioxidant and antibacterial activities; significantly by P. odorata acetone extract. This extract was also chosen due to its comparable MIC and MBC values with both the positive controls respectively. A total of 12 fractions were separated from the extract, however only H05 fraction showed bactericidal action against all gram-positive bacteria. This fraction could also alter the magnitude of bacterial negativity, significantly against MRSA. This data was supported by morphological alterations induced in treated MRSA, through SEM images. The GCMS analysis of H05 fraction showed that the presence of seven major phenolic compounds derivatives that met the Lipinski’s Rule of Five were present in the H05 extract. Among the seven compounds, the MD trajectory analysis showed that 6- hydroxy-8-methoxyoctanoic acid (tannins derivatives) shows strongest and most stable binding with PBP protein. The present study indicates that phenolics mainly tannins present in the P. odorata acetone extract were highly responsible for its antibacterial potential, especially for MRSA infection treatment.