Identification and antimicrobial activity of the sesquiterpene lactone mixture extracted from Smallanthus sonchifolius dried leaves

The present study aimed to identify and screen the antibacterial activity of a mixture of sesquiterpene lactones (SLs) obtained from the dichloromethane extract of Smallanthus sonchifolius leaves. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella enterica strains were used as bacterial tests. The identification and quantification of compounds were established by GC/MS and 1H, 13C 2D NMR spectroscopic analysis. The antimicrobial activity was measured by the disk diffusion method and minimal inhibitory concentration assay (MIC). In vitro antimicrobial assays showed that the mixture of SLs found (uvedalin and enhydrin) displays poor antibacterial activity against the Gram-negative bacteria and appreciable antibacterial properties against the Gram-positive bacterial strain tested when 90 µg of the SLs mixture per disk was used. The MIC determination against S. aureus revealed that a concentration of 750 µg of SLs mixture mL−1 should be necessary to inhibit the strain. These results indicate that the SLs mixture of enhydrin and uvedalin from yacon leaves presents promising antibacterial properties against S. aureus and apparent lack of activity against the Gram-negative bacterial strains tested at the concentrations applied.