Antibacterial activity of ethanolic and aqueous extracts of Acacia aroma Gill. ex Hook et Arn
Introduction
The genus Acacia, one of the important genera of the family Fabaceae (Sub family Mimosaceae) includes aproximately 1350 species and is abundant in Australia, Africa, India and America. The Acacia species are of immense value for reforestation and reclamation of wastelands (Skolmen, 1986), for fuel wood, timber, shelter belts and soil improvement (Palmberg, 1981). Most of its species yield excellent firewood and some are rich sources of protein, tannin, paint, ink, flavouring agents, pulpwood and gum. From the ecological point of view, they can adapt to extremes of temperature, moisture stress and therefore, can be grown in both arid and moist regions in a wide range of tropical soils. Some are also engaged in symbiotic relationship with Rhizobium and mycorrhizal fungi thereby increasing soil fertility. A number of secondary metabolites have been reported from various Acacia species including amines and alkaloids, cyanogenic glycosides, cyclitols, fatty acids and seed oils, fluoroacetate, gums, non protein amino acids, terpenes, hydrolyzable tannins, flavonoids and condensed tannins (Seigler, 2003). However, the secondary metabolites of only a small proportion of Acacia species have been examined in detail. Cytotoxic activities have been reported for Acacia angustissima and Acacia pennatula (Popoca et al., 1998). Otherwise, Acacia nilotica has been traditionally used for ailments such as diarrhea and was reported to have antihyperglycemic (Akhtar and Khan, 1985), antimicrobial (Abd-El-Nabi, 1992), molluscicidal (Hussein, 1984), antihypertensive and antiplatelet aggregatory activities (Shah et al., 1997). A potent cyclooxygenase-1 inhibition by extracts of A. ancistrocarpa was observed (Li et al., 2003).
Acacia aroma Gill.ex Hook et Arn, common name tusca (Burkart, 1952), a native species of Argentina, is member of genus Acacia subgenus Acacia, widely distributed in the provinces of Tucumán, Salta, Santiago del Estero, Catamarca, La Rioja, Formosa, Chaco, Córdoba, San Luis and Santa Fe. A.aroma belongs to the phyto-geographical formation of the Neotropical region, Provincia Chaqueña (Cabrera, 1971). This plant is used in Argentine folkloric medicine as wound healing, antiseptic and for the treatment of gastrointestinal disorders. Leaf and bark infusions have diuretic, anti-inflammatory and cicatrizant uses. Its fruits are important components in the diet of the animals living in this area. Available literature indicates that no previous studies have been carried out on the biological properties of this plant. Phytochemistry studies on Acacia aroma indicated that the main components of the steam volatile flower oils were methyl salicylate and eugenol (Lamarque et al., 1998). Furthermore, fatty acid profiles of A. aroma seed were examined (Lamarque et al., 2000).
Recently, the acceptance of traditional medicine as an alternative form for health care and the development of microbial resistance to the available antibiotics has led authors to investigate the antimicrobial activity of medicinal plants Scrinivasan et al., 2001, Kumarasamy et al., 2002, Ali et al., 2001, Masika and Afolayan, 2002, Hamill et al., 2003. At present, staphylococci and enterococci among Gram-positive bacteria, some enterobacteria and non fermenter organisms such as Pseudomonas aeruginosa and Acinetobacter spp, are recognized as important nosocomial pathogens.
The purpose of the present study was to investigate the antimicrobial activity of leaf, stem and flower extracts of A. aroma against Gram-positive and Gram-negative bacteria. The selected bacteria were antibiotic resistant or multi-resistant human pathogens. The extracts with the highest antibacterial effectiveness were chosen for subsequent use in pharmaceutical formulations.
Section snippets
Plant material
The plants used for the present study were collected from September to March in Trancas, Tucumán, Argentina. For future reference, voucher specimens were deposited in the Herbarium of the Institute de Estudios Vegetales (IEV), Facultad de Bioquı́mica, Quı́mica y Farmacia, Universidad Nacional de Tucumán, Tucumán, Argentina). The parts used were leaves, stems and flowers.
Preparation of Acacia aroma extracts
Lixiviation (fluid extract): ground air-dried plant material was extracted with a 60% or 70% ethanol (v/v) solvent for leaves
Results
Crude extracts of Acacia aroma prepared according to Farmacopea Argentina (decoction, tincture, fluid extract and alcoholature) were compared for their antibacterial activity.
All extracts were analyzed for total phenolic compound content. The yield of water and ethanol soluble principle extractions was determined (Table 1).
Discussion
The obtained results indicate a difference in antimicrobial activity among the extracts. The agar diffusion bioassay showed that leaf and flower fluid extracts have the highest activity against all Gram-positive bacteria and they also showed good activity against Gram-negative bacteria. This is in agreement with observations by other authors Ali et al., 2001, Masika and Afolayan, 2002, Chattopadhyay et al., 2002. The reason for different sensitivity between Gram-positive and Gram- negative
Acknowledgements
This research was partially supported by the Consejo de Investigación de la Universidad Nacional de Tucumán, Argentina, and by the Consejo Nacional de Investigaciones Cientı́ficas y Técnicas, Argentina.
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Career researchers from the Consejo Nacional de Investigaciones Cientı́ficas y Técnicas (CONICET). Buenos Aires, Argentina.