Screening of lab-lab,selected mangrove plant and seaweed for antimicrobial compounds

Abstract

The present study aimed to find out the feasibility of using mangrove leaf, “lab-lab” and seaweed as a bioactive compound source and to evaluate the antibacterial activity of each in vitro against pathogenic bacteria. In vitro screening of the extracts of the seaweed viz., Gracilaria corticata, and the mangrove Avicennia officinalis by disc diffusion test showed species specific activity in inhibiting the growth of bacteria pathogenic to fish viz., Pseudomonas spp., Bacillus megaterium, Aeromonas hydrophila, Salmonella spp. and also E.coli. The solvents used were butanol, methanol, chloroform, acetone and water. The aqueous extracts of A. officinalis leaves showed very high activity against Bacillus, Salmonella and Aeromonas, the zones of inhibition being greater than or comparable to that obtained with the broad spectrum antibiotic chloramphenicol used in the study as a positive control. The butanol extract of mangrove leaf was active against E. coli. The butanol and aqueous extract of the bark of A. officinalis showed good activity against Salmonella and Bacillus, whereas in case of Gracilaria corticata, butanol, chloroform and acetone extracts showed considerable activity against Aeromonas, Salmonella and E. coli, respectively. However, extracts of “lab-lab” in the different solvents did not show any activity against the bacteria tested. Water was the best solvent to extract the antimicrobial compounds from the mangrove leaves while butanol was the best solvent medium for extracting the effective antimicrobial compounds from the marine algae Gracilaria. Phyto-chemical analysis of the aqueous extract of Avicennia leaves by thin layer chromatography to analyze the compound responsible for the antibacterial activity indicated the presence of a polyphenolic lipid quinone with isoprenoid side chains. Thus, present study shows the potential of using mangrove and seaweed extracts for development of antibacterial agents for use in aquaculture as an alternative to antibiotics.