Antibacterial activity of aqueous and ethanol extracts of mangrove species collected from Southern Sri Lanka

Objective: To study the antibacterial activity of mangrove extracts against clinical isolates of Shigella sp., Pseudomonas sp. and antibiotic resistant bacteria, Staphylococcus aureus and Proteus sp. Methods: Crud aqueous and ethanol extracts of mature leaves, tender leaves, bark and shoot of mangroves species (Avicennia marina, Bruguiera gymnorhiza, B. sexangula, Rhizophora mucronata, R. apiculata, Derris trifoliata, Exoecaria agallocha, and Lumnitzera racemosa) were tested for antibacterial activity using agar diffusion method. Results: Both aqueous and ethanol extracts showed considerable activity against all tested bacterial species. However, all the ethanol extracts showed higher inhibition activity than those of aqueous extracts. For both aqueous and ethanol extracts, inhibition zones were larger for non- antibiotic resistant bacteria Shigella sp. and Pseudomonas sp. than antibiotic resistant S. aureus than and Proteus sp. Charcoal treated plant extracts of Avicennia marina, Bruguiera gymnorhiza and Rhizophora mucronata were able to inhibit both clinical isolates of bacterial species more than those of untreated plant extracts. The most clear antibacterial activity was shown by almost plant extracts of Lumnitzera racemosa for both bacterial strains. Mature, young leaf and bark extracts of Exoecaria agallocha also showed considerable antibacterial activity while Derris trifoliata did not show relatively good antibacterial activity. Conclusion: Potential antibacterial activity of both aqueous and ethanol of mangroves suggests, these extracts could be used as an alternative source for treatment of infections caused by these pathogenic bacteria.