Synergy of antibacterial and antioxidant activities from crude extracts and peptides of selected plant mixture.

Sekaran Muniandy,Koshy Philip,Abdul-Mushin M Shami

doi:10.1186/1472-6882-13-360

Sekaran Muniandy, Koshy Philip + Show 1 more

Open Access

https://doi.org/10.1186/1472-6882-13-360

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Abstract

BackgroundA plant mixture containing indigenous Australian plants was examined for synergistic antimicrobial activity using selected test microorganisms. This study aims to investigate antibacterial activities, antioxidant potential and the content of phenolic compounds in aqueous, ethanolic and peptide extracts of plant mixture.MethodsWell diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays were used to test antibacterial activity against four pathogenic bacteria namely Staphylococcus aureus, Escherichia coli, Bacillus cereus, and Pseudomonas aeruginosa. DPPH (2, 2-diphenyl-1- picrylhydrazyl) and superoxide dismutase (SOD) assays were used to evaluate antioxidant activity. HPLC and gel filtration were used for purification of the peptides. Scanning electron microscope was applied to investigate the mode of attachment of the peptides on target microbial membranes.ResultsAqueous extraction of the mixture showed no inhibition zones against all the test bacteria. Mean diameter of inhibition zones for ethanol extraction of this mixture attained 8.33 mm, 7.33 mm, and 6.33 mm against S. aureus at corresponding concentrations of 500, 250 and 125 mg/ml while E .coli showed inhibition zones of 9.33 mm, 8.00 mm and 6.66 mm at the same concentrations. B. cereus exhibited inhibition zones of 11.33 mm, 10.33 mm and 10.00 mm at concentrations of 500, 250 and 125 mg/ml respectively. The peptide extract demonstrated antibacterial activity against S. aureus, E. coli and B. cereus. The MIC and MBC values for ethanol extracts were determined at 125 mg/ml concentration against S. aureus and E. coli and B. cereus value was 31.5 mg/ml. MIC and MBC values showed that the peptide extract was significantly effective at low concentration of the Australian plant mixture (APM). Phenolic compounds were detected in hot aqueous and ethanolic extracts of the plant mixture. Hot aqueous, ethanol and peptides extracts also exhibited antioxidant activities.ConclusionsIt was concluded that APM possessed good antibacterial and antioxidant activities following extraction with different solvents. The results suggest that APM provide a new source with antibacterial agents and antioxidant activity for nutraceutical or medical applications.

Highlights

A plant mixture containing indigenous Australian plants was examined for synergistic antimicrobial activity using selected test microorganisms
It was concluded that Australian plant mixture (APM) possessed good antibacterial and antioxidant activities following extraction with different solvents
The results suggest that APM provide a new source with antibacterial agents and antioxidant activity for nutraceutical or medical applications

Summary

Introduction

A plant mixture containing indigenous Australian plants was examined for synergistic antimicrobial activity using selected test microorganisms. An Australian plant mixture (APM) that contains four indigenous Australian plants (Backhousia citriodora, Terminalia ferdinandiana, Citrus australasica and Lophopyrum ponticum commonly known as Australian wheatgrass sprouts) was examined for synergistic antimicrobial activity using selective test microorganisms. One of these plants is the lemon myrtle or lemonscented iron wood, B. citriodora of the Myrtaceae family. B. citriodora has been used as a food ingredient, food flavouring agent and herbal tea [8] It contains essential oils and two main isomeric aldehydes, cis and trans-citral [9,10]. The aqueous, ethanol and hexane extracts of B. citriodora leaves inhibited the growth of Enterococcus faecalis, P. aeruginosa, E. coli, S. aureus, Salmonella typhi, S. typhimurium and Listeria monocytogenes [12]

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