THE ANTIMICROBIAL ACTIVITY OF ETHANOLIC EXTRACTS DERIVED FROM LEAVES AND PSEUDOBULBS OF COELOGYNE FLACCIDA LINDL. (ORCHIDACEAE) AGAINST DIFFERENT STAPHYLOCOCCUS AUREUSSTRAINS

Abstract

The present study was conducted to investigate in vitro antimicrobial activity of ethanolic extracts obtained from leaves and pseudobulbsof Coelogyneflaccida against Staphylococcus aureus subsp. aureus Rosenbach (ATCC®25923™) (mecA negative), Staphylococcus aureus subsp. aureus Rosenbach (ATCC®29213™)(mecA negative, Oxacillin sensitive, weak β-lactamase-producing strain), Staphylococcus aureus NCTC 12493 (mecA positive, Methicillin-resistant, EUCAST QC strain for cefoxitin).The antimicrobial susceptibility testing was done on Muller-Hinton agar by the disc diffusion method (Kirby-Bauer disk diffusion susceptibility test protocol). The leaves and pseudobulbs of C. flaccida plants, cultivated under glasshouse conditions, were sampled at M.M. Gryshko National Botanic Garden (NBG), National Academy of Science of Ukraine. Freshly leaves and pseudobulbs were washed, weighed, crushed, and homogenized in 96% ethanol (in proportion 1:19) at room temperature. The extracts were then filtered and investigated for their antimicrobial activity. The cultivation medium was trypticase soy agar (Oxoid™, UK), supplemented with 10% defibrinated sheep blood. Cultures were grown aerobically for 24 h at 37°C. The cultures were later diluted with a sterile solution of 0.9% normal saline to approximate the density of 0.5 McFarland standard. The McFarland standard was prepared by inoculating colonies of the bacterial test strain in sterile saline and adjusting the cell density to the specified concentration. The examined ethanolic extracts obtained from leaves and pseudobulbs of C. flaccida showed remarkable antibacterial activities against different S. aureusstrains. The observed activity may contribute to the reasons why orchids are used for infectious and inflammatory conditions in ethnomedicine. The research showed that ethanolic extracts of C. flaccida possess the highest antibacterial potency against S. aureus NCTC 12493 strain. These findings led the authors to suggest that these extracts may be used as natural antiseptics and antimicrobial agents in medicine and veterinary practice. Nevertheless, despite the promising results, more research should be carried out to further evaluate the roles of particular compounds, isolated from all parts of orchid plants, attributable to antimicrobial activity.