Polar Extracts from (Tunisian) Acacia Salicina 'Lindl. Study of the Antimicrobial and Antigenotoxic Activities
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BMC Complementary and Alternative Medicine
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Polar extracts from (Tunisian) Acacia salicina 'Lindl. Study of the antimicrobial and antigenotoxic activities
BMC Complementary and Alternative Medicine 2012, 12:37 doi:10.1186/1472-6882-12-37
ISSN Article type Submission date Acceptance date Publication date Article URL
1472-6882 Research article 3 September 2011 10 April 2012 10 April 2012 http://www.biomedcentral.com/1472-6882/12/37
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Polar extracts from (Tunisian) Acacia salicina ‘Lindl. Study of the antimicrobial and antigenotoxic activities
Jihed Boubaker1† Email: jihed.boubaker@yahoo.fr Hedi Ben Mansour1† Email: hedi.mansour@hotmail.fr Kamel Ghedira2 Email: kamel.ghedira@gmail.com Leila Chekir Ghedira1,3* Corresponding author Email: leila.chekir@laposte.net
* 1
Laboratory of Cellular and Molecular Biology, Faculty of Dental Medicine, University of Monastir, Rue Avicenne, Monastir 5000, Tunisia
2
Unity of Pharmacognosy/ Molecular Biology, Faculty of Pharmacy, University of Monastir, Rue Avicenne, Monastir 5000, Tunisia
3
Department of Cellular and Molecular Biology, Faculty of Dental Medicine, Rue Avicenne, 5000 Monastir, Tunisia †These authors equally contributed to this work.
Abstract
Background
Methanolic, aqueous and Total Oligomer Flavonoids (TOF)-enriched extracts obtained from the leaves of Acacia salicina ‘Lindl.’ were investigated for antibacterial, antimutagenic and antioxidant activities.
Methods
The antimicrobial activity was tested on the Gram positive and Gram negative reference bacterial strains. The Mutagenic and antimutagenic activities against direct acting mutagens, methylmethane sulfonate (MMS) and 4-nitro-o-phenylenediamine (NOPD), and indirect acting mutagens, 2-aminoanthracene (2-AA) and benzo[a]pyrene (B(a)P) were performed with S. typhimurium TA102 and TA98 assay systems. In addition, the enzymatic and nonenzymatic methods were employed to evaluate the anti-oxidative effects of the tested extracts.
Results
A significant effect against the Gram positive and Gram negative reference bacterial strains was observed with all the extracts. The mutagenic and antimutagenic studies revealed that all the extracts decreased the mutagenicity induced by B(a)P (7.5 µg/plate), 2-AA (5 µg/plate), MMS (1.3 mg/plate) and NOPD (10 µg/plate). Likewise, all the extracts showed an important free radical scavenging activity towards the superoxide anion generated by the xanthine/xanthine oxidase assay system, as well as high Trolox Equivalent Antioxidant Capacity (TEAC), against the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS)+• radical. TOF-enriched extract exhibited the highest protective effect against free radicals, direct acting-mutagen and metabolically activated S9-dependent mutagens.
Conclusions
The present study indicates that the extracts from A. salicina leaves are a significant source of compounds with the antimutagenic and antioxidant activities, and this may be useful for developing potential chemopreventive substances.
Background
Plants are rich source of natural products used for centuries to cure various diseases. The plant-derived medicines are based upon the premise that they contain natural substances that can promote health and alleviate illness. So, a retrospection of the healing power of plants and a return to natural substances are an absolute need of our time. The demonstration of the presence of natural products, such as polyphenols, alkaloids, flavonoids, coumarins and other secondary metabolites in medicinal plants will provide a scientific validation for the popular use of these plants [1]. Acacia (Fabaceae) is an evergreen tree that is native of Australia, but it is now widely distributed in the Mediterranean area. Acacia is a large genus comprising more than 700 species. The genus Acacia is frequently used for the treatment of various illnesses because of their reputed pharmacological effects; published informations indicate that Acacia has hypoglycemic [2], antibacterial [3], anti-inflammatory [4], cestocidal [5], spasmogenic and vasoconstrictor [6], antihypertensive and antispasmodic activities [7], anti-aggregation platelet effect [8], as well as an inhibitory effect against hepatitis C virus [9]. In Tunisian traditional medicine, the use of Acacia differs according to the species and according to the region. Based on informations gathered from traditional healers, herbalists, and inhabitants of rural south Tunisia, Acacia salicina has frequently been used as a the treatment of several diseases, such as the treatment of inflammatory diseases, as "febrifuge" to treat cancer, and as a fertility enhancer. In the south Tunisia, infusions prepared from fresh or dried leaves are taken orally, or alternatively, chopped fresh leaves are applied directly on inflamed sores. Traditional medical uses of Acacia in the north Tunisia are somewhat different [10].
Some Acacia species, and among them Acacia salicina, were described to be rich in tannins. Tannins obtained from A. salicina were reported to be responsible for the microbial activity [11]. Hence, in this paper we examined the antimicrobial, antimutagenic, and antioxidant activities of polar extracts obtained from Acacia salicina leaves. Our study revealed an interaction between the secondary metabolite composition of extracts, and each radical and/or bacterial strain used in the different assays.
Results and discussion
Antimicrobial activity
The antibacterial activity of the three tested A. salicina leaf extracts was evaluated on five pathogenic bacteria. Our results showed that these extracts exhibited various levels of antibacterial effect against all the tested bacterial strains. Minimum Inhibitory Concentration (MICs) values ranged from 0.0625 to over 10 mg/ml, and Minimum Bactericidal Concentration (MBCs) values ranged from 0.125 to more than 10 mg/ml. Generally, TOF extract displayed a strong activity against both Gram-negative and Gram-positive bacteria. The result of the antimicrobial activity is presented in Table 1. Table 1 Antibacterial activity of Acacia salicina extracts, expressed as Minimum Inhibitory Concentration (MIC) and as Minimum Bactericidal Concentration (MBC) Gram positive organisms (mg/mL) S. aureus E. faecalis ATCC25923 ATCC25922 MIC MBC MIC MBC Gram negative organisms (mg/mL) E. coli S. enteritidis S. typhimurium ATCC 25922 ATCC 13076 NRRLB 4420 MBC MIC MBC MIC MBC MIC 7.5 5 0.5* 0.26
Extracts a Metanolic 1 2.5 2.5 5 > 10 > 10 2.5 5 2.5 extract Aqueous extract 1.25* 2.5 2.5 5 2.5 5 2.5 5 2.5 TOF extract 0.0625* 0.125* 0.25* 0.5* > 10 > 10 0.25* 0.5* 0.125* Ampicilin b 0.0015 0.225 0.0025 0.125 0.006 0.275 0.0019 0.085 0.0039 * P 10 mg/ml respectively. Compared to ampicillin, used as a positive control against S. aureus (0.225 mg/ml), the tested TOF extract was twice more active with MBC value of 0.125 mg/ml. E. coli was found to be the least sensitive strain to A. salicina extracts. Compared to the other extracts, TOF extract was the most active one against all the tested bacterial strains. Its biological efficiency is probably related to the high amounts of
flavonoids and polyphenolic compounds, in its chemical composition. We previously reported, that A. salicina extracts, particularly TOF extract, contains flavonoidic, polyphenolic and coumarinic compounds [12]. These families of compounds are reported to play a role in the prevention of colonisation by parasites, bacteria and fungi [13]. Our results indicate that Gram-positive bacteria are more sensitive to the antimicrobial effect of A. salicina extracts than Gram-negative ones. It is interesting to note that A. salicina extracts exhibited an antimicrobial activity, particularly towards organisms of interest to the medical field such as Staphylococci, Enterococci and Salmonella. In fact, Salmonella remains a primary cause of food poisoning worldwide, and massive outbreaks have been reported in recent years. The centre for disease control and prevention estimated that approximately 1.4 million cases of salmonellosis were annually reported in the United States [14]. The European Union reported more than 100.000 cases of salmonellosis [15]. In Tunisia, between 1978 and 1993, 1022 Salmonella strains were isolated: 578 in hospitals and 444 from the environment [16]. Some pathogenic Salmonella serotypes adapted to man, such as S. typhimurium, usually cause severe diseases such as enteric fever in humans. However, some pathogenic Salmonella serotypes, such as S. enteritidis or S. typhimurium, can infect a wide range of hosts and are termed ubiquitous. Likewise, foodborne illness resulting from the consumption of food contaminated with pathogenic bacteria, has been a vital concern to public health. Salmonella spp. and E. coli accounted for the largest number of outbreak cases and deaths.
Antioxidant activities Radical-Scavenging activity against ABTS+
The free radical scavenging capacity of A. salicina extracts was evaluated using the ABTS assay (Table 2). Decolorization of ABTS+• reflects the capacity of antioxidant species to donate electrons or hydrogen atoms to inactivate this radical cation. A potential activity was noted at the different tested concentrations of all the studied extracts. The tested extracts seem to be more active than the positive control, trolox compound, as IC50 value obtained with trolox (0.76 mg/ml) was higher than IC50 value obtained with TOF, methanol and aqueous extracts (0.11, 0.39 and 0.24 mg/ml respectively). In fact, the tested extracts are complex mixtures of several compounds, in particular phenolic compounds with diverse chemical structures that determine various properties. The antioxidant effect of polyphenols against ABTS+. was reported earlier [17,18], similar to our observations in the current study. The reaction pattern consists of initial fast scavenging activity, where more active compounds react immediately with the radical. Products are formed, and together with the less reactive molecules, give a second slow reaction. The results obtained with our extracts corroborate this type of kinetic behaviour in all the samples and dilutions assayed. According to the result reported in the Table 2.
