Abstract

The localization of bioactive phytochemical(s) may be one of the important approaches for the containment of antibiotic resistance. This study evaluated the antibacterial activity and toxicity of crude extracts and fractions from Urtica dioica L. Successive extraction of the leaves with hexane, chloroform, ethyl acetate and methanol; and their screening for antibacterial activity by disc diffusion assay against five strains each of fish and human bacteria, was assessed. Hexane extract showed good antibacterial activity; hence it was further fractionated using silica gel column chromatography into 30 sub fractions which were pooled together according to their thin layer chromatography (TLC) profile to give overall 5 sub fractions. Among the 5 sub fractions, fraction-2 (HF2) showed the highest antibacterial activity with minimum inhibitory concentration (MIC) values ranging from 31.25 to 250 µg/mL against both the fish and human pathogens, determined by serial tube dilution method. The  toxicity tests with Artemia salina showed that the all the solvent extracts of U. dioica along with HF2 showed a higher margin of safety with LC₅₀ value of >1000 μg/mL each. Gas chromatography–mass spectrometry (GC-MS) analysis of HF2 showed neophytadiene (19.96%), 2,6,10,15-tetramethylheptadecane (12.82%), heptadecyl ester (9.45%), hexyl octyl ester (6.31%), 2,7,10-trimethyldodecane (5.60%), butyl tetradecyl ester (4.73%), octadecan-1-ol (4.45%), 1,2-benzenedicarboxylic acid (4.38%), 4,6-di-tert-butyl-m-cresol (4.32%) and 2,4-ditert-butylphenol (4.30%), constituting 75.36% of the total peak area percentage, as the major constituents. Our results showed that the leaves of U. dioica are an interesting source of biologically active compounds that may be applied for the treatment of infectious diseases in both human as well as veterinary animals.

Key words: Artemia salina, gas chromatography–mass spectrometry (GC-MS), minimum inhibitory concentration (MIC), toxicity.