Abstract:
Mangrove plants and their major chemical classes were reported to possess biological effects. Therefore it is worth to screen mangrove plants extracts for the presence of new antibacterial compounds. Bacterial pathogens which affect aquatic animals and humans become resistant to antibiotics due to long term exposure. This study focused on the antibacterial efficacy of six species of mangroves (Avicennia marina, Lumnitzera racemosa, Bruguiera sexangula, Acanthus ilicifolius, Rhizophora mucronata, Excoecaria agallocha) against four pathogenic bacteria, Pseudomonas fluorescens, Pseudomonas aeruginosa, Shigella flexneri and Listeria monocytogenes. Most effective inhibitory activity shown mangrove plant was evaluated again by using its different parts. Mangrove parts extracts were obtained using 95% methanol as a solvent and the final compound was methanol free due to evaporation. Antibacterial susceptibility tests were carried out by using well diffusion assay method. The results were compared with Tetracycline as the positive control and solvent without extract as a negative control. Mangrove leaves extracts were effective against all bacterial pathogens tested except Shigella flexneri. It was resistant against Tetracycline and moderately susceptible for all mangrove leaves extracts (7.4 mm — 12.3 mm). The tested mangrove leaves extracts were effective against aquatic bacterial pathogens used (p < 0.5) in vitro. Rhizophbra mucronata parts extracts (root, bark, fruit and flower) also exhibited positive inhibition zones for all the tested bacterial species cultured in vitro (p < 0.5). Rhizophora leaf, root and bark extracts possessed higher antibacterial potential when compared to the fruit and flower extracts. Rhizophora leaf extracts showed highest inhibition for Listeria monocytogenes(18.8 ±1.04) and Pseudomonas fluorescens (17.8 ± 0.41) while root and bark extracts were effective against Shigella flexneri (15.0 ± 0.88) and Pseudomonas aeruginosa (16.1 ± 0.51) respectively. Rhizophora root extract has MIC value of (15 mgml-1) against Listeria monocytogenes and (25 mgm1-1) against Pseudomonas aeruginosa. The results provided evidence that, the mangrove extractions of Rhizophora mucronata have antibacterial activity, particularly in the leaf extract, which can be used to treat aquatic bacterial pathogens as an environmental friendly natural compound.Key words: Antibacterial resistance, Fish bacterial pathogens, Mangroves extracts, Minimum Inhibitory Concentration, Rhizophora mucronata.
