Antibacterial And Antifungal Activity Of Buckinghamia Celsissima Leaf Extracts

摘要

The antimicrobial activity of a methanolic extract of Buckinghamia celsissima leaves was investigated by disc diffusion assay against a panel of bacteria and fungi. B. celsissima leaf extractinhibited the growth of 5 of the 14 bacteria tested (36%). Gram-positive and Gram-negative bacteria were both affected by B. celsissima extract although Gram-positive bacteria were more susceptible. 3 of 11 Gram-negative (27%) and 2 of the 3 Gram-positive bacteria tested (67%) had their growth inhibited by B. celsissima extract. B. celsissima leaf extractdisplayed antifungal activity towards Candida albicans when tested by disc diffusion assay and inhibited the growth of the yeast Saccharomyces cerevisiae.The antibacterial activity of B. celsissima leaf extractwas further investigated by growth time course assays which showed significant growth inhibition in cultures of Bacillus cereus,Bacillus subtilis, Pseudomonas fluorescens and Aeromonas hydrophilia within 1 h. Introduction Plants contain many biologically active compounds which have potential for development as medicinal agents. Herbal medicines already form the basis of therapeutic use in developing countries but recent years have also seen an increase in the use of herbal medications in the developed world as well. Some studies focusing on the investigation of traditional African (Kudi et al., 1999; Okeke et al., 2001), Caribbean (Chariandy et al., 1999) and Indian (Ahmad and Beg, 2001) medicinal plants have resulted in the identification of new sources of therapeutic agents. Antimicrobial multiple drug resistance toward commonly used commercial drugs has resulted in an increase in the search for antimicrobial agents from natural sources. Plant derived antimicrobial agents are a largely untapped resource with enormous medical potential and much more investigation is needed in this area. As a result of its isolation, Australia has a variety of unique and distinctive flora not found elsewhere in the world. Australian Aborigines used a variety of plant medicines to help maintain their health prior to European settlement (Barr et al., 1993; Lassak and McCarthy, 1993). More than 150 plants from nearly 60 widely varied botanical families were used by Australian Aborigines as antiseptic agents (Lassak and McCarthy, 1993). Although there is enormous potential for the development of medicinal agents from Australian plants, much of our knowledge of the antimicrobial activity of Australian plants is anecdotal. Recent studies (Palombo and Semple, 2001; Cock, 2008a) have demonstrated the antibacterial activity of extracts from a number of Australian plants. Buckinghamia celsissima (ivory curl tree) is a flowering tree of the family Proteaceae. It is endemic to the rainforests of north-eastern Australia. A recent study (Cock, 2008a) has demonstrated the antibacterial activity of methanolic extracts of B. celsissima extracts against a limited panel of bacteria. The current study was undertaken to validate and extend these observations against a wider panel of bacteria and fungi. Materials and Methods Plant Collection and ExtractionThe extracts investigated in this study have been described previously (Cock, 2008a,b). Briefly, B. celsissima leaves were collected from verified trees in the suburbs of Brisbane, Australia. B. celsissima leaves were dried in a Sunbeam food dehydrator and the dried material was ground to a coarse powder. 1 g of each of the powdered leaves was extracted extensively in 50 ml methanol (Ajax, AR grade) for 24 hours at 4 oC with gentle shaking. The extract was filtered through filter paper (Whatman No. 54) under vacuum followed by drying by rotary evaporation in an Eppendorf concentrator 5301. The resultant pellet was dissolved in 15 ml 20 % methanol. The extract was passed through 0.22 μm filter (Sarstedt) and stored at 4 oC.Test MicroorganismsAll media was supplied by Oxoid Ltd. All microbial strains were obtained from Tarita Morais, Griffith University. Stock cultures of