ANTIMICROBIAL ACTION OF MANGROVE PLANT EXTRACTS AGAINST SALMONELLA TYPHI AND CANDIDA PARAPSILOSIS CHARACTERISED BY THEIR ANTIOXIDANT POTENTIALS AND BIOACTIVE COMPOUNDS

Plants present in the mangrove ecosystem are underexplored for their natural bioactive agents, including a neglected scope of inventing newer antimicrobials, to combat global crisis mediated by MDR microorganisms. In this study, we investigated four plants-Excoecaria agallocha, Bruguiera gymnorhiza, Avicennia alba and Aegialitis rotundifolia of the Sundarbans, world’s largest mangrove ecosystem in West Bengal, India, for their antimicrobial activities against Salmonella typhi and Candida parapsilosis, in addition to their important bioactive resources including antioxidants. Ethanolic, methanolic, and DMSO extracts of leaves of these plants were studied by antimicrobial screening, determination of total phenolic and flavonoid contents, DPPH free radical scavenging activity, ABTS [2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)] assay, ferric reducing antioxidant power (FRAP), lipid peroxidation inhibition, thin layer chromatography, and liquid chromatography-mass spectroscopy (LC-MS). E. agallocha extracts showed excellent antimicrobial activities against S. typhi, while antifungal activity against C. parapsilosis was almost lacking. MIC values of all the extracts against S. typhi was as low as 3.96 µg/mL, however, growth inhibition was most with E. agallocha extract. Again total phenolic content (>300 mg/g), DPPH scavenging activity (75.55%), ABTS scavenging (78.53%), lipid peroxidation inhibition (64.35%) activities were found highest with E. agallocha extract. All chemicals retrieved by LC-MS of E. agallocha were found bioactive, among them hexanoylglycine, chorismic acid, tyramine, methyl jasmonate, khayanthone, chlorogenic acid were found particularly important. This study undoubtedly pointed out a good quality natural reservoir of important antimicrobials, antioxidants, and bioactive chemicals in the mangrove plants studied by us, predominantly in E. agallocha, which emerged a candidate mangrove plant for industrial development for such chemicals.