Ethnobotanical Leaflets 12: 433-438. 2008.
Screening of Certain Ethnomedicinal Plants for Antibacterial Activity
P. Murugan, A.Rajesha, T. Athiperumalsami and V.R. Mohan*
Ethnopharmacology unit, Research department of Botany
V.O.Chidambaram college.Tuticorin. Tamilnadu.
aDepartment of Botany, Annamalai University, Annamalai Nagar, Tamil Nadu.
*Corresponding Author e mail:[email protected]
Issued 25 June 2008
Benzene, petroleum ether, chloroform, methanol and aqueous extracts of five plant species, traditionally used for treatment of ailments of infectious nature were screened for in vitro antibacterial activity against different species of bacteria, Staphylococcus aureus, Streptococcus lactis, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi. Antibacterial activity was tested using the disc diffusion method. Most of the activity detected was against Gram positive bacteria.
Medicinal plants are still major parts of traditional medicinal systems in developing countries. Many infectious diseases are known to be treated with herbal remedies throughout the history of mankind. Even today, plant materials continue to play a major roll in primary health care as therapeutic remedies in many developing countries. (Zakaria, 1991). Medicinal plants, which form the backbone of traditional medicine, have in the last few decades been the subject of very intense pharmacological studies. This has been brought about by the acknowledgement of the value of medicinal plants as potential source of new compounds of therapeutic value and as source of new compounds in drug development.
In many parts of the world medicinal plants are used for antibacterial, antifungal and antiviral activities. Plant derived drugs serve as a prototype to develop more effective and less toxic medicines. Tribal medicine has not been studied extensively. Hence, an attempt has been made to study the in vitro antibacterial activity of five ethnomedicinal plants used by tribals in Grizzled Giant Squirrel Wildlife Sanctuary, Tamil Nadu.
Materials and Methods
Ethnomedicinal information and plant collection
Information on usage presented in this paper was based on literature surveys presented in Table 1. Plant materials Bauhinia purpurea L., Cardiospermum helicacabum L., Cissampelos pareira L., Rhinacanthus nastus (L.) Kurz. var. nastus and Swertia corymbosa Wighti were collected from the well grown plants found in the natural forest of Grizzled Giant Squirral Wildlife Sanctuary, Srivilliputhur, Western Ghats, Tamil Nadu. The collected plant materials were shade dried at room temperature for 10-15 days.
Extraction of plant material
Various organic solvents were used for the extraction of bioactive compound. The leaf/ stem powder (10g) was first extraction with petroleum ether for defatting in a Soxhlet apparatus. The defatted powdered residue was dried and successively extracted with benzene, petroleum ether, chloroform, methanol and Aqueous then water in a Soxhlet apparatus. The extracts obtained were completely evaporated by using vacuum rotary evaporator. The final weight of the various crude extracts were weighted and prepared the concentration.
Bacterial strains of Staphylococcus aureus, Streptococcus lactis, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi were procured from Microbial type culture collection, Chandigarh. The bacteria were incubated on a nutrient agar-slant (Stationary cultures) for 48h at 37oC followed by inoculation in Mueller Hinton Agar (MHA) medium.
Antibacterial activity was demonstrated using a modification of the method originally described by Bauer et al. (1966) which is widely used for the antibacterial susceptibility testing (Barry and Thornsberry, 1985). A loopful bacteria was taken from the stock culture and dissolved in 0.1ml of saline. All the tests were done by placing the disc (6mm diameter) impregnated with (20µl) various crude solvent extracts on the Mueller Hinton Agar surface previously inoculated with 10ml of MHA liquid medium with Gram positive and Gram negative bacteria. Respective solvents without plant extracts served as negative control. Standard antibiotics of chloramphenicol (30µg/disc) and tetracycline (30µg/disc) were used as reference or positive control. Plates were incubated at 37oC for 24 hours. After the incubation period, the diameter of the inhibition zone around the plant extracts saturated discs were measured and also compared with the diameter of inhibition zone of commercial standard antibiotic discs.
Results and Discussion
The results of the antibacterial activity of the plant extracts were tabulated in Table 2. A total of 50 extracts from 5 different plant species were investigated. All the extracts have exhibited different degrees of antibacterial activity against the tested bacteria; among them leaf extract showed broad spectrum activity against Bacillus subtilis and Pseudomonas aeruginosa. Leaf extract of Rhinacanthus nastus var. nastus showed activity against all the test pathogenic bacteria. Antibacterial activity was found in the methonal extracts of Swertia corymbosa leaves, benzene extracts of Swertia corymbosa stem, both benzene and methanol extracts of leaves and stems of Bauhinia purpurea, Rhinocanthus nastus var nastus, stem of Cardiospermum halicacabum.
Most antibacterial activity was found against the Gram positive bacteria. Forty four extracts were found to be active against Gram positive bacterium Bacillus subtilis, 40 against Streptococcus lactis 39 against Staphylococcus aureus. The inhibition zone diameters were compared with antibiotics drugs Chloramphenicol and tetracycline in table 3 as a standard reference.
These observations suggested that the aqueous and organic extracts from the same plants showed different activities. There are no common rules for this, but in most cases, the organic extracts showed the same or greater activity than the aqueous extracts. In addition, the effectiveness of plant was not due to one main active constituent, but to the combined action of the chemical compound involved in it. This study has identified five plants with some antibacterial activity. This finding lends some support to traditional knowledge and can serve as a basis for selecting the most active medicinal plants to use in traditional medicine practices in the future.
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Table1. Ethnobotanical data of studied plants.
Table 2. Antibacterial activity of various solvent extracts on some ethnomedicinal plants.
a Microorganisms: Sa, Staphylococcus aureus; Sl, Streptococcus lactis; Bs, Bacillus subtilis, Pa, Pseudomonas aeruginosa; Ec, Escherichia coli; St, Salmonella typhi;
b Extraction/Solvent used: I, Petroleum ether; II, Benzene; III, Chloroform; IV, Methanol; V, Water.
Table 3. Antibiotic reference standards.