Introduction

Plants have long history of medicinal and antibiotic usage, dating back to 4000BC (Nickel, 1959). Medicinal and aromatic plants constitute a major source of natural organic compounds widely used in medicines, food products, cosmetics and paints that are of importance in everyday life. More than 2000 medicinal plants were  found to be existing in India and  out of this about 500 varieties are used in Siddha and Ayurvedic medicine. The study supports the view that several ethanomedicinal plants might be useful as antimicrobial agents resulting in the development of novel drugs for many centuries through ethno pharmacology (Heinrich, 2000; Heinrich and Simon, 2001). Ethanol extracts of Terminalia balleria, Garcinea gummigulla, Anisomeles malabarica, Aegle marmelos, Alangiumsa lurifolium and Zigibus jujube showed antibacterial activity against Bacillus subtilis,  Staphylococcu auerus and Eschericia coli (Anderson et.al., 1997).

Material and Methods

Collection of sample

Plants such as  Acalypha indica, Achyranthes aspera, Aegle marmelos, Andrographis paniculata and Leucas aspera were selected and the leaves were used for the study.

Preparation of solvent extract

The leaves of the selected   five plant  species were separately washed, shade dried and crushed. The powder was subjected to extraction by Soxhlet method using petroleum ether at 60-80˚C for 8 hours. The resulting petroleum ether crude extracts were concentrated to a paste and stored in air tight containers for further use

Collection of test organisms

Three bacterial cultures  such as Eschericia coli, Staphylococcus aureus and Proteus spp were collected from Bose laboratory, Madurai, Tamil Nadu, India and  were used as  test organisms.

Antibacterial Activity (Kirby – Bauer disc diffusion technique)

Antibacterial activity of the leaf extracts were tested against the three bacterial cultures using Nutrient agar medium. Nutrient agar plates were prepared and the cultures were spread individually on the plates. Antibiotic discs were prepared using Whattman No 1 filter paper. The discs of 6mm dia  was dipped in extract, dried for 15minutes and placed on bacterial culture swabbed plates and the plates were incubated at 37^◦C for 24hrs. Zone of inhibition around the disc indicates the susceptibility of the test organism. The following  mixed plant extracts were also screened for synergistic effect against  the three selected bacteria using the Kirby – Bauer disc diffusion method for 24 hours and 48 hours. Plant extract mixtures tested  are:

a) A. marmelos + L. aspera(1:1)

b) A. marmelos + A. paniculata, (1:1)

c) A. marmelos + A. indica(1:1)

d) A. marmelos + A. aspera(1:1)

Result and discussion

Medicinal and aromatic plants constitute a major source of natural organic compounds widely used in medicines (Dobhal, 1994). Hence the ethno botanical approach is being applied to the search for new drugs. The antibacterial activity of the  five selected plant leaves were tested against three organisms(E.coli, S. aureus and  Proteus spp) at  two different incubation period  i.e 24 and 48h and the results are tabulated in Table 1 and 2 respectively. The 24hrs antibacterial activity of the five selected plant extracts indicating the zone of inhibition of growth reveals that E.coli is susceptible against all the five plants  extracts  tested at both 24 and 48h incubation period and it was followed by S. aureus   and Proteus sp. Similar result was observed by Anderson et.al, (1997) in E. coli with the ethanol extracts of Aegle marmelos.In the present study among the  four mixtures tested for the  antibacterial activity against the  three bacterial strains the zone of inhibition was higher for E.coli in all the four plant mixtures tested at 24 and 48h(Table3 and Table 4) and it was followed by S.aureus and Proteus sp.

Table 1: Antibacterial activity of the five selected plant extracts indicating the zone of inhibition of growth (in cm) at 24 hours

Table 2: Antibacterial activity of the five selected plant extracts indicating the zone of inhibition of growth (in cm) at 48 hours

 Table 3: Synergistic efficacy of Aegle marmelos with the other four selected extracts against the test bacteria indicating zone of inhibition of growth in cm (24h)

Table 4: Synergistic efficacy of Aegle marmelos with the other four selected extracts against the test bacteria indicating zone of inhibition of growth in cm (48h)

The study shows that there is scope for using the selected plants for the treatment of the bacterial species tested and plant mixtures are better than the individual plants.

Reference

1. Anderson,A.,Valsaraj,R., Puspangadan, P., Smith, U.W., Nyman,U.1997. Antimicrobial screening of selected medicinal plants from India. Journal of Ethonopharmacology. V. 58 (2); 75-83
2. Heinrich, M. 2000.  Ethobotany and its role in drug development. Phytother. Res . 14:479- 488.
3. Heinrich, M. and Simon Gibbon, 2001. Ethonopharmacology in drug development discovery: an analysis of its role and potential contribution. J. Pharmacol .53; 425-432.
4. Dobhal, R. 1994. Medicines and aromatic Plants. Curr Sci. 66(6): 397-398.
5. Nickel,L.G.,1959. Antimicrobial activity of vascular plants. Economic Botany 13:281-318.