Ethnobotanical uses, phytochemical and antimicrobial investigation of Nymphaea lotus L. growing in the Zambezi region, Namibia

Nymphaea lotus L. is an aquatic perennial plant with significant ethnobotanical, socio-economic and environmental importance. This study evaluated its ethnobotanical uses, phytochemical composition, and antimicrobial properties. An ethnobotanical survey was conducted in the Zambezi region between December 2018 and April 2019. Antimicrobial activity of dichloromethane: methanol (DCM:MeOH) extracts of N. lotus flowers were tested against Candida albicans, Saccharomyces cerevisiae, Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Clostridium perfringens, Enterococcus faecalis, Escherichia coli, Salmonella typhimurium, Shigella sonnei, Pseudomonas aeruginosa, and Proteus vulgaris. These assessments employed disc diffusion, broth dilution, time-kill assays, and time-kill synergy methods. Ethnobotanical findings indicated that N. lotus is traditionally used for food seasoning and preservation. The antimicrobial mode of action of N. lotus flower extracts was confirmed through the leakage of electrolytes and the release of cellular materials absorbing at 260 and 280 nm. The DCM:MeOH extracts exhibited antimicrobial activity against all tested foodborne pathogens. The Independent-Sample Kruskal-Wallis test revealed no statistically significant differences between the minimal inhibitory concentration (MIC) and the 50% growth inhibition (IC₅₀) values (p = 0.100 and p = 0.170, respectively). Further analysis confirmed that the extracts caused leakage of electrolytes, nucleic acids, and proteins from the tested pathogens. The total phenolic (302.5±0.03 mg GAE/g) and total flavonoid content (2106.8±0.04 mg CAE/g) indicate the presence of bioactive phytochemicals in N. lotus flowers. These findings suggest that N. lotus has potential as a natural preservative for controlling foodborne pathogens and may also serve as a functional food supplement to help combat malnutrition.