Evaluation of antibacterial activity of different mangrove plant extracts

P.D. Abeysinghe, R.N. Pathirana, R.P. Wanigatunge


Antibacterial activity of mature leaves, tender leaves and bark extracts of Avicennia marina, Avicennia officinalis and Bruguiera sexangula were evaluated using Soxhelt extraction method. Petroleum ether, chloroform, ethyl acetate and ethanol were used as solvents in order to get the plant extracts. The antibacterial activity was screened by using agar diffusion technique against pathogenic bacteria species of Staphylococcus sp. (from urine), Proteus sp. (from a wound), Escherichia coli (from infected blood), Shigella sp. (from a wound) and Pseudomonas sp. (from a wound). The length of inhibition zone was measured in millimeters from the edge of the well to the edge of the inhibition zone. Twelve different plant extracts in A. marina, A. officinalis and B. sexangula exhibited different degree of growth inhibition against tested bacterial strains. Mature leaf extracts of A. marina and tender leaf extracts of A. officinalis in ethyl acetate exhibited promising antibacterial activity than other plant extracts. All plant extracts in ethyl acetate showed strong inhibition compared to other extracts on all tested bacterial strains. Among all bacterial strains, Pseudomonas sp. and E. coli showed considerable growth inhibition against almost all plant extracts. Mature leaf extract of only A. marina was used for further investigations since a large amount of tender leaves of A. officinalis was not readily available. Charcoal treated mature leaf extracts of A. marina showed more inhibition for all tested bacterial strains than untreated plant extracts. Combinations of mature leaf extracts of A. marina in different solvents failed to exhibit synergistic activity against tested bacterial strains. Most combinations showed antagonistic effect against Proteus sp., E. coli and Shigella sp. Antibacterial activity of plant extracts of A. marina gradually declined during 4 months after extraction, for all tested bacterial strains. Components of mature leaf extracts of A. marina in chloroform, ethyl acetate and ethanol were separated by Analytical Thin Layer Chromatography (ATLC) when the eluents were hexane and diethyl ether. Isolated components in Preparative Thin Layer Chromatography (PTLC) exhibited moderate antibacterial activity against Pseudomonas sp., Shigella sp. and E. coli. Separated components did not show any antibacterial activity against Proteus sp. and Staphylococcus sp. Phytochemical screening revealed that mature leaf of A. marina contained alkaloids, steroids, triterpenoids and flavonoids.

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