Journal of Traditional Medicine & Clinical Naturopathy
Open Access

Traditional herbal medicines play an important role in the health care systems of many countries. In India, the natives implement various herbs formulation for curing various ailments. The preparation and administration of drugs varies from place to place [1]. An Ethnomedicinal study offers immense opportunities to develop new drugs. Being closer to nature, traditional societies had gained knowledge regarding the use of wild flora and fauna, mostly unknown to the urban, who are away from the natural ecosystem [2].

Nicobarese are still living their customary way of life, especially those in Little Nicobar, Chowra and Teressa Islands, while the life in Nancowry, Kamorta, Katchal, Great Nicobar and Car Nicobar is on the verge of extinction due to modernization [3]. Tribal communities of Andaman and Nicobar Islands, especially the Nicobarese, depend on plant resources to prepare herbal medicines, for food, making household implements, as a sleeping mat and for fire. The former possess a great emporium of ethnobotanical wealth, as they are still isolated from the modern way of life and are still closer to nature [4].

This article reports the results of antimicrobial properties of eighteen medicinal plants elected from previous surveys that was done based on ethnomedicinal practices among the Nicobarese tribes of the Andaman and Nicobar Islands [3,5]. These results are continuation work of bioassay tests for antimicrobial and antimalarial activities medicinal plants of Andaman and Nicobar Islands [6,7].

Plant materials

Plants were selected for this study based on their medicinal use and availability to the TKPs during the field survey. Fresh plant parts were collected from the tribal villages of Car Nicobar with the help of TKPs (Table 1).

Table 1: List of ethnomedicinal plants collected for antimicrobial screening.

Microorganisms

The microorganisms used in this study included three bacterial strains and one fungal strain. These were Proteus mirabilis (MTCC 425), Shigella flexneri (MTCC 1457), Salmonella enterica typhi (MTCC 733), and fungal strain Aspergillus niger (MTCC 282), which were procured from Microbial Type Culture Collection, Chandigarh, India.

Extraction of plant materials

The leaves of plants were separately dried under shade, pulverized by a mechanical grinder and passed through 40-mesh sieve to obtain a fine powder. Hundred grams of coarsely powdered dry leaves were extracted by cold percolation method with 95% methanol as solvent, for 72 hours at room temperature. The whole plant extract was collected in a conical flask, filtered and the solvent was evaporated to dryness under reduced pressure in an Evaporator (Eppendroff 5304) at 40-45°C. The residues were stored at 4°C for future use.

Antimicrobial susceptibility

The agar well diffusion method was used to screen the antimicrobial activity [8]. The Mueller Hinton Agar plates and Saboard Dextrose Agar were prepared by pouring 15 ml of molten media into sterile petriplates for bacterial and fungal strains respectively. The plates were allowed to solidify for 5 minutes. To this 0.1% inoculum suspension was swabbed uniformly, and allowed to dry for 5 minutes. Wells were dug in agar plates with the help of sterile metallic borer (diameter=8 mm). 50 μl of various extracts were poured into the wells which were marked previously and kept for incubation at 37°C aerobically for 18 h bacteria and 48 h for fungi. At the end of incubation period, inhibition zones formed around the disc were measured in millimeter, using a transparent scale. Data are expressed as the means ± SEM.

In the assay against four pathogenic microorganisms, 7 plants extracts showed antimicrobial activity by inhibiting one or more microorganisms. Among the plants screened, M. citrifolia, and B. rotunda showed promising activity against tested microorganisms (Table 2).

Table 2: Antimicrobial activities of the selected ethnomedicinal plants.

M. citrifolia, B. rotunda and G. calocarpum produced largest zones of inhibition against S. typhi and S. flexeneri. The most sensitive bacterium was S. typhi which was inhibited by methanol extract of five plants followed by S. flexeneri and P. mirabilis.

Methanol extracts of G. calocarpum, M. oleifera, P. corymbosa and U. lobata, also showed anti-bacterial activity. Only the methanol extract of leaves of S. alata showed antifungal activity but no activity against bacterial strains used in the study.

Research reports clearly indicate that the M. citrifolia plant has antitubercular effect, anti-cancer properties, anti-oxidant properties, anti-inflammatory activity, antidiabetic activity etc. [9]. B. rotunda used in Nicobarese traditional medicine for the treatment of stomachache, diarrhoea and fever. It is also reported the presence of polyphenols constituents, antioxidants and anticancer activities [10,11].

Antibacterial activity of G. calocarpum is reported for the first time. No previous report on the antibacterial activity of this plant could be found in the literature.

Senna alata showed antifungal activity against A. niger. In the previous findings roots and the leaves of S. alata showed a range of activity against several bacteria and fungi. In this study methanol extract of leaves of S. alata showed only antifungal activity and no activity against bacterial strains used in the study.

The results indicate that scientific studies carried out on medicinal plants having traditional claims of effectiveness might warrant fruitful results. Several plants exhibit some degree of antimicrobial activity towards the human pathogens used in the study. Phytochemical studies are required to determine the types of compounds responsible for the antibacterial effects of these species.

The authors acknowledge to the Indian Council of Medical Research (ICMR), New Delhi, India for providing financial grant for the study (Project No. Tribal/43/2008-ECD-II).