Purification and characterisation of phytochemicals extracted from Rhizophora mucronata: Their efficacy against Pseudomonas aeruginosa infection in Catla catla

Abstract The aim of this work is to purify and characterise bioactive molecules from various solvent extracts prepared with the leaves of Rhizophora mucronata, a mangrove plant. In vitro assessment of antibacterial activity of n-hexane, diethyl ether, ethanol, and aqueous extracts (AEs) against Bacillus subtilis (0.4 ± 0.1, 1.1 ± 0.3, 0.9 ± 0.1, and 1.2 ± 0.7 mm), Staphylococcus aureus (1.2 ± 0.1, 2.3 ± 0.5, 3.2 ± 1.2, and 4.4 ± 1.7 mm), Klebsiella pneumoniae (0.5 ± 0.3, 1.7 ± 0.4, 3.9 ± 1.4, and 3.9 ± 0.9 mm), and Pseudomonas aeruginosa (0.2 ± 0.1, 2.5 ± 0.6, 3.7 ± 0.5, and 4.2 ± 1.3 mm) has proven to act as potent similar to that of commercial antibiotic. Corresponding to antibacterial activity result, antioxidant activity was also higher for AE (75.97% ± 0.5%) compared to remaining extracts (73.77% ± 2.5%, 69.99% ± 0.4%, and 65.24% ± 1.8%) at a concentration of 500 μg·mL−1. Considering both the activities, AE was selected for separation of bioactive molecule by deploying two purification techniques – column chromatography and preparative thin layer chromatography consecutively. After purification, the sample was injected into mass spectrometer and the presence of N-p-coumaroyltyramine and luteolin with excellent antibacterial and antioxidant properties (13.1 ± 2.2 mm and 80.9% ± 2.3%, respectively) were recognised. Further, in vivo investigations on Catla catla fingerlings infected with P. aeruginosa indicated that partially purified extracts cured the infection and resulted in a 100% survival rate.