Antibacterial mode of action of the hydroethanolic extract of Leonotis nepetifolia (L.) R. Br. involves bacterial membrane perturbations

作者：Oliveira Darley Maria; Melo Fernanda Germano; Balogun Sikiru Olaitan; Flach Adriana; Alexandre de Souza Edineide Cristina; de Souza Gilmar Prado; Araujo Rocha Iolanda do Nascimento; Mendonca Alves da Costa Luiz Antonio; Soares Ilsamar Mendes; da Silva Larissa Irene; Ascencio Sergio Donizeti; de Oliveira Martins Domingos Tabajara

来源：Journal of Ethnopharmacology, 2015, 172: 356-363.

DOI：10.1016/j.jep.2015.06.027

• Leonotis nepetifolia
• Lamiaceae
• Antimicrobial
• Phytochemistry
• Flavonoids
• Phenolics

Ethnopharmacological relevance: Leonotis nepetifolia (L) R. Br., Lamiaceae, a pantropical shrub, popularly known in Brazil as "cordao-de-frade", "rubim", is reportedly used in Brazilian ethnomedicine as well as in different countries in the treatments of ailments such as infections, inflammations, wounds, stomach disorders, among others.
Aim of the study: To evaluate its potential cytotoxicity and antibacterial mode of action of the hydroethanolic extract of L nepetifolia (HELn) leaves, including phytochemical analysis.
Materials and methods: The cytotoxicity of HELn was investigated by Alamar blue assay, using CHO-K1 cells. Antibacterial activity of HELn was tested by broth microdilution methods against a panel of bacteria of clinical interest. The mode of action of L neperifolia was studied by targeting bacterial membranes. Phytochemical analysis was performed by determining total secondary metabolites with spectrophotometric assays and HPLC.
Results: HELn is not cytotoxic in the in vitro evaluation (IC50 > 200 pg/mL). It demonstrated a good spectrum of antibacterial activity with major activity against Shigella flexneri, Enterococcus faecalis, Staphylococcus aureus and Bacillus subtilis with MIC = 6.25 gg/mL, Helicobacter pylori with MIC of 2514/mL and Streptococcus pyogenes with MIC of 50 lig/mL. Its mode of action is associated, at least partly, with changes in the permeability of bacterial membranes, as evidenced by the increased entry of hydrophobic antibiotics in Shigella flexneri and intense efflux of K and nucleotide leakage in E. faecalis and Shigella flexneri. In addition, the presence of phenols, flavonoids and carotenoids, described in the literature to possess antibacterial effects, were detected in the composition of HELn, with high phenol content (11.55%), especially the flavonoids (6.47%).
Conclusion: The results indicate that HELn has low cytotoxicity and potent antibacterial activity. It is bacteriostatic in nature, possibly acting at the level of bacterial membranes, especially on the cytoplasmic membrane and outer membrane, thus supporting its popular use in infectious processes. In addition, the presence of phenols, flavonoids, carotenoids, fatty acids and steroids, described in the literature as possessing antimicrobial activity, were detected in the composition of HELn.

• 出版日期2015-8-22