Introduction. Antibiotic resistance is one of the greatest threats of the 21st century. Scientists search for potential antimicrobial\nsources that can cope with antibiotic resistance. Plants used in traditional medicine can be identified as potential candidates for the\nsynthesis of novel drug compounds to act against antibiotic-resistant bacteria. Objective. To determine the potential antimicrobial\neffects of ethanol, aqueous, and hexane extracts of five Sri Lankan medicinal plants against four human pathogens. Methods.\nAsparagus falcatus (tubers), Asteracantha longifolia (whole plant), Vetiveria zizanioides (roots), Epaltes divaricata (whole plant),\nand Coriandrum sativum (seeds) were used in the study. Plant extracts were screened against four clinically important Grampositive\nand Gram-negative bacterial strains, Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), Pseudomonas\naeruginosa (ATCC 27853), and Klebsiella pneumoniae (ATCC 700603). Antibacterial activity of plant extracts were monitored\nusing the agar disc diffusion method. Eight concentrations of each positive plant extract were used to determine the minimum\ninhibitory concentration (MIC) by 5-fold dilution of plant extracts yielding a serial dilution of the original extract. Results.\nEthanol, aqueous, and hexane extracts of E. divaricata gave the maximum zones of inhibition of 16.3 mm, 7.4 mm, and 13.7mm\nand MIC values of 0.48 mg/ml, 1.2 mg/ml, and 1.6 mg/ml, respectively, against S. aureus. Ethanol and hexane extracts of V.\nzizanioides gave the maximum zones of inhibition of 12.1mm and 11.4mm and MIC values 2.4 mg/ml and 0.003 mg/ml, respectively,\nagainst S. aureus. None of the other plants were effective against any microorganism used for the study. Conclusions. It\ncan be concluded that E. divaricata and V. zizanioides crude ethanol, aqueous, and hexane extracts exhibited significant in vitro\nantibacterial activity against S. aureus, and the active compounds isolated from them can be potential sources for the synthesis of\nantibacterial drugs.
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