Evaluation of in vitro antioxidant activity of Nelumbo nucifera leaf extract and its potential application as antibacterial agent against fish pathogens

The aim of this study was to determine the antioxidant and antibacterial property of Nelumbo nucifers (lotus) leaf extract. Total phenolic content and DPPH (2, 2-diphenyl-1-picrylhydrozyl) scavenging methods were used to evaluate the antioxidant property of crude extract. DPPH scavenging capacity of extract varied significantly (p<0.05) depending on the concentration, except 5.5mg/ml and 7 mg/ml concentrations. The maximum concentration (10mg/ml) of the extract showed the highest scavenging effect (57.75%). The phenolic contents exhibited a similar trend to that of DPPH. Total phenolic compounds increased with the increasing concentration of N. nucifera leaf extract. Disc diffusion and broth micro-dilution methods showed bactericidal property of lotus leaf extract. Water, acetone-water and ethanol-water based extracts were tested against selected gram-positive (Staphylococcus aureus) and gram-negative (Aeromonas hydrophila, Pseudomonas fluorescens) bacterial pathogens of fish. The broth micro-dilution method with TTC (2, 3, 5-triphenyl tetrazolium chloride) to indicate the viability of aerobic bacteria was found to be the best alternative method.