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Sequential extracts of some medicinally important arid zone plants of Rajasthan, viz. Lepidagathis trinervis Nees., Polycarpea corymbosa Lam. and Sericostoma pauciflorum Stocks. ex Wight. were tested against six bacterial (Gram +ve and Gram –ve) and five fungal strains using agar well diffusion method. Ethyl acetate extract of L. trinervis showed maximum activity against Bacillus subtilis, Enterobactor aerogenes, Pseudomonas aeruginosa, Aspergillus flavus and Trichophyton rubrum (inhibition zone 16.00±0.81, 13.33±0.66, 14.33±1.85, 14.30±0.34 and 23.00±0.00 mm) at varied minimum inhibitory concentrations of 82, 20, 41, 41 and 20 μg/ml, respectively.
Lepidagathis trinervis Nees (Acanthaceae) is a prostrate to sub-erect, up to 30 cm tall undershrub and its ashes were used to cure eczema. L. trinervis shows anticancer activity against L1210 lymphoid leukemia and hypotensive effect. Polycarpea corymbosa Lam. traditionally used in venomous bites from reptile, jaundice and on inflammatory swellings[3,4]. Some sterols such as α-1 barrigenol, camelliagenin A and stigmasterol have been isolated. Sericostoma pauciflorum Stocks ex Wight (Boraginaceae) is a short straggling undershrub growing widely throughout sea coast of Saurashtra and Maharashtra. It is generally used in dehydration and acidity. Phytochemically, fernane, hopane and other type of triterpenoids were isolated from the plant[6–8].
Whole plants of each were collected from the fields locally during the months of October to January, 2007-08. The botanical identity was confirmed by Herbarium, Department of Botany, University of Rajasthan, Jaipur. Voucher specimens of the plants have been deposited at the Herbarium and Laboratory for further reference. Each of 100 g air-dried, powdered plant materials was Soxhlet extracted separately for 72 h in petroleum ether, dichloromethane, ethyl acetate, methanol and water in increasing order of polarity. The different extracts were concentrated and dried using vacuum evaporator to give solid residue and were stored at 40, until use.
For antimicrobial screening, Gram +ve bacteria (Bacillus subtilis MTCC 441; Staphylococcus aureus MTCC 740) and Gram -ve bacteria (Escherichia coli MTCC 443; Pseudomonas aeruginosa MTCC 741; Enterobacter aerogens MTCC 111 and Raoultella planticola MTCC 530), obtained from IMTECH, Chandigarh, were used. The bacterial strains were maintained on nutrient agar medium. Further, fungi namely Aspergillus niger (ATCC 322), A. flavus (ATCC 16870), Candida albicans (ATCC 4718), Trichophyton rubrum (ATCC 2327) and Penicillium crysogenum (ATCC 5476) obtained from IARI, New Delhi, were used. These fungal strains were maintained on Sabouraud dextrose agar (SDA) medium.
Antimicrobial screening was performed by agar well diffusion method using Müller-Hinton medium for antibacterial and SDA medium for antifungal activity. In the culture plates, wells were prepared with the help of sterile cork borer (6 mm in diameter) and 4 mg extract were delivered per well. Plates were incubated at 370for bacteria and 250in case of fungi for 24 h under aerobic conditions. The diameter of the inhibition zone (IZ) around each hole was measured by inhibition zone recorder (HiMedia) in triplicate and statistically analyzed.
Agar well diffusion method was used for the determination of MIC of crude plant extracts. Serial dilutions of the extracts ranging 2000 μg to 20 μg were prepared and administered in previously inoculated plates. Gentamycin (10 μg/ml) in case of bacteria and ketoconozole (100 units/ml) in case of fungi were used as standard antibiotics.
Among Gram + ve bacteria, maximum activity was exhibited by L. trinervis ethyl acetate extracts against B. subtilis (IZ 16.00±0.81 mm, MIC 82 μg/ml; Table 1) and P. corymbosa petroleum ether extract against S. aureus (IZ 13.66±0.32 mm, MIC 62.5 μg/ml).
In case of Gram -ve bacteria, L. trinervis ethyl acetate extract showed maximum activity against E. aerogens (Inhibition Zone 13.33±0.66 mm, MIC 20 μg/ml) followed by ethyl acetate extract of S. pauciflorum (IZ 15.33±0.33 mm, MIC 82 μg/ml). Ethyl acetate and methanol extracts of L. trinervis exhibited maximum inhibition against P. aeruginosa (IZ 14.33±1.85 mm and 19.33±2.02 mm respectively, MIC 41 μg/ml in both cases). Methanol extract of L. trinervis (IZ 15.33±0.33 mm) and ethyl acetate extract of S. pauciflorum (IZ 11.66±0.66 mm) with MIC of 62.5 μg/ml demonstrated maximum inhibition against R. planticola.
Likewise maximum antifungal activity against A. flavus was demonstrated by dichloromethane and ethyl acetate extract of L. trinervis (IZ 16.00±0.00 mm, 14.30±0.33 mm with MIC 41 μg/ml; Table 2). Petroleum ether extract of S. pauciflorum showed significant inhibitory effect against A. niger (IZ 11.66±0.33 mm, with MIC 62.5 μg/ml). Appreciable activity against T. rubrum was exhibited by dichloromethane and ethyl acetate extracts of L. trinervis (IZ 20.00±0.00 mm and 23.00±0.00 mm, respectively with MIC 20 μg/ml in both cases).
From these results, it is evident that the selected plants demonstrated potential antibacterial and antifungal activities. In literature, L. trinervis, has been known as a bitter tonic and used to cure eczema while P. corymbosa also used in suppression of inflammatory swellings[3,4], as reported elsewhere in Ayurvedic literature, have been further established.
Authors are thankful to the Indian Council of Medical Research, New Delhi, India, for financial support.
Jain, et al: Antibacterial and Antifungal Potentials of Some arid Zone Plants