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. 2013 Dec 16:13:360.
doi: 10.1186/1472-6882-13-360.

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

Abdul-Mushin M Shami, Koshy Philip  1 , Sekaran Muniandy
Affiliations

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

Abdul-Mushin M Shami et al. BMC Complement Altern Med. .

Abstract

Background: A 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.

Methods: Well 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.

Results: Aqueous 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.

Conclusions: It 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.

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Figures

Figure 1
Figure 1
Inhibition zones of ethanolic extract of selected plant mixture on selected test microorganisms. Different letters (a- d) showed significant difference (p < 0.05) from all samples and control (10 mg/ml of Tetracycline) by using one-way ANOVA followed by Duncan’s Multiple Comparison. *All samples in three replicates ± SD.
Figure 2
Figure 2
Inhibition zones of different extracts of selected plant mixture on selected test microorganisms. (A) effect of ethanolic extract of selected plant mixture (EAU) and (B) peptides extracts (PAUS) against selected test microorganisms with different concentration compare to positive control (10 mg/ ml of Tetracycline).
Figure 3
Figure 3
Inhibition zones of peptide extract of selected plant mixture on selected test microorganisms. Different letters (a- d) showed significant difference (p < 0.05) from all samples and control (10 mg/ml of Tetracycline) by using one-way ANOVA followed by Duncan’s Multiple Comparison. *All samples in three replicates ± SD.
Figure 4
Figure 4
Fractionation of peptides extracted from selected plant mixture by sephadex G-75 gel filtration.
Figure 5
Figure 5
DPPH scavenging activity of different extracts of selected plant mixture. The values are the average of three replicates ± SD. The results were analyzed by one-way ANOVA followed by Duncan’s Multiple comparison Test. Different letters (a- c) showed significant difference (p < 0.05) from all samples and control. Positive control indicates to 10 mg/ml of ascorbic acid.
Figure 6
Figure 6
Inhibition rate of SOD activity of different extracts of selected plant mixture. The results were analysed by one-way ANOVA followed by Duncan’s Multiple comparison Test. Different letters (a- c) showed significantly difference (p < 0.05) from all samples and control. Positive control used 10 mg/ml concentration of ascorbic acid.
Figure 7
Figure 7
Effect of peptides extracted from Australian plant mixture (F1) by scanning electron microscope. (A) and (C) control: B. cereus.(B) and (D)B. cereus treated with peptides.
Figure 8
Figure 8
HPLC chromatogram of F1 of selected plant mixture detected at 254, 215 and 280 nm. Active fraction peak was at 4.181 min.
Figure 9
Figure 9
LC - MS/MS analysis of active fraction of APM with amino acid sequences.
See this image and copyright information in PMC

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