Antibacterial activity of organic extracts from Solidago graminifolia leaves

Solidago graminifolia (syn. Euthamia graminifolia (L.) Nutt) is a native species plant from North America, with abundant flavonoids, diterpenes, and polyacetylenes metabolites that have shown cholinesterase enzyme inhibitory activity and antimicrobial activity. The aim of this study was to determine the antibacterial activity of Solidago graminifolia leaf extracts obtained with ethanol, dichloromethane, and hexane solvents. The S. graminifolia extracts were tested against Escherichia coli, Salmonella enterica, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. The chemical composition of each extract was analyzed by UPLC-MS/MS. The yield extracts in ethanolic, dichloromethane and hexanoic solvents were 20.39 %, 18.34 %, and 5.3 %, respectively. The secondary metabolites identified were flavonoids, hyperoxide, quercetin, kaempferol, and some phenolic acids, such as chlorogenic acid and solidagoic acid derivatives. The ethanolic extract inhibited the five strains in all concentrations (15 mg/mL, 10 mg/mL, 5 mg/mL, and 2.5 mg/mL). The ethanol extract has a MIC of 2.0 mg/mL against S. aureus and 1.5 mg/mL for the Gram-negative bacteria E. coli, S. enterica, P. aeruginosa, and K. pneumoniae; the dichloromethane extract has MIC values of 2.5 mg/mL for Gram-negative strains and 2.0 mg/mL for S. aureus. This study showed that the ethanolic extract had the best antibacterial activity, and its biological activity can be attributed to its richness in polyphenolic compounds.