antibacterial activity, australian plants, medicinal plants, methanol extracts
I Cock. Antibacterial Activity of Selected Australian Native Plant Extracts. The Internet Journal of Microbiology. 2007 Volume 4 Number 2.
Thirty nine methanolic extracts from twenty five Australian native plants were investigated for their antibacterial activity against two Gram-positive (
Bacterial resistance to currently used antibiotics is becoming a concern to public health (Monroe and Polk, 2000). The development of bacterial super resistant strains is resulting in currently used antibiotic agents failing to end many bacterial infections. For this reason the search is ongoing for new antimicrobial agents, either by the design and synthesis of new agents, or through the search of natural sources for as yet undiscovered antimicrobial agents (Bhavnani and Ballow, 2000). Herbal medications in particular have seen a revival of interest (Chariandy
Prior to European settlement in Australia, the Aboriginal people used a variety of plant medicines to help maintain their health (Barr
Much of the information about the antimicrobial activities of Australian plants is anecdotal. Few of the Aboriginal medicinal plants have been scientifically investigated for their antimicrobial activities. One study (Palombo and Semple, 2001) examined a panel of plant extracts commonly used by Australian Aboriginals and found approximately 20% of the samples tested were able to inhibit bacterial growth. This group has also demonstrated the antiviral activity of the same Australian plants (Semple
Materials and Methods
Collection of Plant Samples
Preparation of Crude Extracts
Plant samples were dried in a Sunbeam food dehydrator and the dried material was ground to a coarse powder. 1 g of each of the samples of dried plant material
All media was supplied by Oxoid Ltd. Microbial strains were obtained from Tarita Morais, Griffith University. Stock cultures of
Evaluation of Antimicrobial Activity
Antimicrobial activity of each plant extract and was determined using a modified Kirby-Bauer (Bauer
The extracts were tested using 6 mm sterilised filter paper discs. Discs were impregnated with 10 µl of the test sample, allowed to dry and placed onto inoculated plates. The plates were allowed to stand at 4 °C for 2 hours before incubation with the test microbial agents at 30 °C for 24 hours. Following this incubation the diameters of the inhibition zones were measured in millimetres. All measurements were to the closest whole millimetre. Each antimicrobial assay was performed in at least triplicate. Mean values (± standard deviation) are reported in this study. Standard discs of ampicillin (2 µg) and chloramphenicol (10 µg) were obtained from Oxoid Ltd. and served as positive controls for antimicrobial activity. Filter discs impregnated with 10 µl of distilled water were used as a negative control.
Results and Discussion
Thirty nine samples from twenty five Australian native plant species were extracted in methanol, dried and the weight of extracted material recorded (table 1). The weight of dried extractable material varied across samples, ranging from 83 mg (
Antimicrobial activity of the extracts was determined by disc diffusion assays. Twenty nine of the thirty nine extracts tested (72%) showed antibacterial activity against one or more bacteria. Indeed, of the twenty five plant species tested only 3 species had no inhibitory activity towards any of the bacteria tested in any of their extracts (
Gram-positive bacteria (
In contrast to the Palombo and Semple (2001) report, many of the Australian native plant extracts examined in the present report also had significant activity towards Gram-negative bacteria. These differences relate to the different species studied, but may also relate to the extract concentrations tested. Some of the extracts tested in this study were tested at concentrations as high as 30-40 mg extracted material per ml. No mention is made in the Palombo and Semple report (2001) of the concentrations of extracted material tested so the possibility exists that lower doses were used in those studies. However, the concentrations tested in this study were comparable to the 36 mg/ml extracts used by Kudi
Noteworthy was the apparent trend that flower extracts generally were more potent inhibitors of bacterial growth than were leaf extracts from the same plant. In only one case (
The results of this study provide further evidence of the antimicrobial activities of some Australian native plants. This study indicates that
Financial support for this work was provided by the School of Biomolecular and Physical Sciences, Griffith University, Australia.