Screening of plant extracts for their antibacterial activity on human pathogens.
Background: To evaluate the In vitro antibacterial activities of methanolic extracts of medicinal plants Polyalthia longifolia (Sonner) Thw, Parthenium hysterophorus Linn., Citrus limon (L) Burm. f., Quisqualis indica (Linn), Tephrosia Purpurea (Linn) pers, Adhatoda zeylanica Medik, Tinospora cordifolia (Wild) Miers ex Hook. and Thoms, Tribulus terrestris (Linn), Piper longum (Linn), Phyllanthus emblica L. Linn., Abutilon indicum (Linn) sweat, Azadirachta indica A. juss, Mimosa pudica (Linn) and Pongamia pinnata (Linn) Mree. Methods: The antibacterial activity of all the 14 medicinal plants used in the study were tested by agar well diffusion method against 12, (5 gram positive and 7 gram negative) bacterial pathogens. The bacterial susceptibility index (BSI) and average percent of bacterial susceptibility (APBS) was determined for evaluating the antimicrobial activity of plant extracts. Results and discussion: All 14 methanolic plant extracts have shown antibacterial activity. The largest DIZ (Diameter of Inhibition zone) belongs to Polyalthia longifolia leaf extract against Aeromonas hydrophilaas as 23 mm. It has shown an average DIZ of 20 mm against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis. According to BSI Aeromonas hydrophila and Escherichia coli, were most susceptible Gram-negative bacteria having BSI value 100 mm and 64.2 mm respectively and most susceptible Gram-positive were Staphylococcus aureus and Bacillus subtilis with a BSI value of 78.5 mm and 50 mm respectively. APBS for Gram-negative bacteria was 34.6 mm and for Gram-positive bacteria was 25.7 mm showing that the plant extracts are more effective against Gram-negative bacteria than Gram-positive bacteria. Conclusion: The study shows that Polyalthia longifolia, Parthenium hysterophorus, Citrus limon, Quisqualis indica has potent antibacterial activity and are new source for antibacterial compounds for treating drug resistant human pathogen.