Antibacterial and antioxidant properties of flowers from Tecoma stans (L.) Juss. ex Kunth (Bignoniaceae)

Abstract

Tecoma stans (L.) Kunth (Bignoniaceae), is popularly known as ipê-mirim, and used in traditional medicine for the treatment of diabetes and digestive problems. The aim of this work was to evaluate the antibacterial, antioxidant and synergistic potential of the ethanol extract and fractions from the T. stans flowers, and to determine their chemical composition. The hexane fraction (HEX) was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS), and fatty acid esters and the phytosterols could be identified. The ethanol extract (EE), and dichloromethane (DCM), ethyl acetate (EA) and hydroethanol (HE) fractions were analyzed by liquid chromatography coupled to a diode array detector and mass spectrometer (LC-DAD-MS). Alkaloids (tecomine, tecostamine, and coumaroyl-spermidine analogs), O-glycosylated flavones and flavonols (O-glucuronyl O-methyl quercetin, O-hexosyl luteolin, and others), and phenylethanoid glycosides (dihydroxyphenyl ethyl O-caffeoyl O-deoxyhexosyl hexoside, hydroxyphenyl ethyl O-coumaroyl O-deoxyhexosyl hexoside, and others) were identified. The EE with DCM and EA fractions exhibited antioxidant effects, and had the highest levels of phenolic compounds. Regarding Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) tests, the EE, DCM and EA fractions showed potential results against Escherichia coli, E. coli EHEC and Enterococcus faecalis. The EE and DCM and EA fractions interacted synergistically with amoxicillin and tetracycline decreasing the MIC of antibiotics 2–5 fold when compared with the MIC of antibiotics used alone. These results provide a basis for additional studies aimed to evaluate the possibility of using extract or fractions from T. stans as natural sources of antioxidants and antibacterial agents of plant origin.