Evaluation of antimicrobial activity of different solvent extracts of Lawsonia inermis L. leaf against human pathogens

Abstract

The development of drug resistance of pathogens, as well as the appearance of undesirable side effects of certain antibiotics has necessitated the search for new therapeutic agents from natural sources. Keeping this in view, the antimicrobial effect of Lawsonia inermis L. (Lythraceae) leaf extracts were examined using petroleum ether, methanol, and aqueous solvents and tested against 10 human pathogenic bacteria such as Escherichia coli, Bacillus subtilis, Bacillus circulans, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Salmonella typhi, Salmonella paratyphi, Streptococcus mitis, Proteus vulgaris and 6 fungi such as Aspergillus niger, Candida albicans, Candida tropicalis, Candida krusei, Fusarium oxysporum and Trychophyton mentagrophytes. Agar well diffusion method was adopted to test the susceptibility of the test microorganisms to the plant extracts while minimum inhibitory concentration (MIC) was determined using serial dilution of extracts. Petroleum ether extract of L. inermis leaf showed the highest antibacterial activity (zone of inhibition diameter in mm) against Salmonella typhi (40.11±0.01) followed by Salmonella paratyphi (26.03±0.06), Proteus vulgaris (19.03±0.06) and Staphylococcus aureus (14.13±0.0). Methanol extract of L. inermis leaf showed significantly higher activity against Streptococcus mitis, followed by Bacillus circulans, Proteus vulgaris (zone of inhibition diameter in mm was found to be 25.07±0.06, 23.03±0.05 and 22.07±0.06, respectively), but aqueous extract of L. inermis had higher inhibitory activity against the Salmonella typhi, Pseudomonas aeruginosa (26.06±0.05 and 19.06±0.05 mm zone of inhibition) than the rest of bacteria. Both methanol and petroleum ether leaf extract of L. inermis showed higher inhibitory activity against Candida krusei, Fusarium oxysporum, Trichophyton mentagrophytes (zone of inhibition diameter in mm was found to be 36.1±0.01, 36.07±0.06, 26.14±0.02, (M) and 35.06±0.03,31.08±0.02,24.08±0.02 (P), respectively) than Candida albicans and Candida tropicalis. Aqueous extract of L. inermis showed the inhibitory activity against Candida tropicalis, Candida krusei, Fusarium oxysporum, Trychophyton mentagrophytes (zone of inhibition diameter in mm was found to be 23.1±0.01, 23.07±0.06, 21.06±0.05, and 19.07±0.06, respectively) and least was found for Candida albicans, while the Aspergillus niger did not respond to any extract. Antibiotics such as Ampicillin, Ciprofloxacin, Streptomycin and Tetracycline used for bacteria and antifungals like Fluconazole, Terbinafine, Itraconazole, Chloramphenicol (0.5 mg/ml) were used as positive controls and compared with the plant extracts tested. Minimum inhibitory concentration was observed within the range from 6.25-50 mg/ml against all microbes. The results of the present study indicated that Lawsonia inermis L. leaf extracts can suitably be exploited for developing new antibiotics (herbal antibiotics) to overcome the increasing bacterial and fungal resistance to synthetic drugs.