Phytochemical analysis of Brasolia, Elleanthus, and Sobralia. Three genera of orchids with antibacterial potential against Staphylococcus aureus

Max Rykaczewski , Mirosława Krauze-Baranowska , Jerzy Żuchowski , Marta Krychowiak-Maśnicka , Jakub Fikowicz-Krośko , Aleksandra Królicka

Abstract

The purpose of the study was to determine the chemical composition of extracts from three species of orchids: Brasolia cattleya, Elleanthus oliganthus and Sobralia powellii, all belonging to the Sobralieae tribe, evaluate their antistaphylococcal activity and assess possible toxicity towards eukaryotic cells on the model organism Caenorhabditis elegans. The chemical composition of the methanolic extracts from those plants was tested with the use of UHPLC-ESI-MS/MS method. The phytochemical analyses of the extracts revealed presence of three main groups of secondary metabolites: phenolic derivatives, flavonoid glycosides and triterpenoid saponins. In our studies, the presence of C-O-glycosides of methoxylated flavones and ester derivatives of arbutin were found for the first time in the Orchidaceae family. The extracts were investigated for antimicrobial activity against five Staphylococcus aureus strains, including four strains isolated from hospital patients. The antimicrobial activity of the orchid extracts was estimated by the Minimum Inhibitory Concentration (MIC) and the Minimal Bactericidal Concentration (MBC) determined by Broth Microdilutions method. All of the examined extracts showed strong antimicrobial activity against the S. aureus strains. The MBC values ranged from 0.25 to 0.75 mg of fresh weight (fw)/mL. To assess the toxicity of the extracts we used cultures of C. elegans, wild-type N2 Bristol strain. The extracts occurred to be nontoxic towards C. elegans in a broad range of concentration (from 0.75 mg to 50 mg fw/mL) after 24-hour incubation. The maximum extract dose tested on C. elegans was 10 times higher than the effective bactericidal concentration for S. aureus. The obtained results allow us to conclude that the methanolic extracts from B. cattleya, E. oliganthus and S. powellii are of a potential use for treatment of bacterial infections caused by the antibiotic-resistant strains of S. aureus.