Antituberculosis, antibacterial and antioxidant activities of Aegiceras corniculatum, a mangrove plant and effect of various extraction processes on its phytoconstituents and bioactivity

Natural products have traditionally provided a rich source of drugs for many diseases, and novel phytochemicals are the most widely used natural products as therapeutic agents. A plethora of novel and structurally diverse compounds have been reported from different mangrove species. This may be due to the constant biotic and abiotic stress under which mangroves grow. Different methods have been explored for extraction of phytoconstituents, each method having its own advantages. The current research work thus explores the activity of leaf extract of Aegiceras corniculatum (a mangrove plant) against Mycobacteria and other micro-organisms. Different extraction techniques were employed to check their effect on the antituberculosis activity. Microwave assisted extraction showed an MIC of 19.53 μg/ml against Mtb H37Rv strain in vitro using Resazurin Microtitre Assay (REMA), in comparison to 39.06 μg/ml and 1250 μg/ml for soxhlet and maceration techniques respectively. The microwave and soxhlet crude extracts were then fractionated using different solvents and these fractions were tested for their antituberculosis activity in vitro. The MIC ranged from 6.25 μg/ml to 100 μg/ml for the different fractions. The ethyl acetate fraction of microwave extract showed the most active MIC of 6.25 μg/ml compared to the other fractions. Interestingly, the same fraction also showed the highest phenolic content and also the highest antioxidation potential. The fractions showed negative correlation for antituberculosis activity with phenolic content showing that, the more the phenolic content, the less is the MIC i.e. more potent. The crude extracts were also tested against M. smeg and at the concentration of 5 mg/ml, the extracts showed very low activity with percentage death being 54.42%, 53.61% and 38.51% for microwave, soxhlet and maceration respectively. Against E. coli, percentage death was found to be 79.86%, 77.65% and 49.50% and against B. subtilis, percentage death was 47.19%, 46.61% and 31.02% for microwave, soxhlet and maceration extracts respectively. The extracts thus display selective inhibition against Mtb and can be explored further for identification of the phytoconstituents showing anti-tuberculosis activity.