RESEARCH ARTICLE Open Access Antimicrobial and antioxidant flavonoids from the leaves of Oncoba spinosa Forssk. (Salicaceae) Marie Geneviève Djouossi 1 , Jean-de-Dieu Tamokou 2* , David Ngnokam 1 , Jules-Roger Kuiate 2 , Leon Azefack Tapondjou 1 , Dominique Harakat 3 and Laurence Voutquenne-Nazabadioko 4 Abstract Background: Naturally occurring flavonoids have been reported to possess various pharmacological properties. The aim of this study was to evaluate the antimicrobial and antioxidant activities of the MeOH extract and flavonoids from the leaves of Oncoba spinosa, a plant used for the treatment of syphilis, wounds and sexual impotence. Methods: The plant extract was prepared by maceration in methanol and sequentially fractionated by column chromatography. The structures of isolated compounds were elucidated on the basis of spectral studies and comparison with published data. The MeOH extract and its isolated compounds were evaluated for their antibacterial and antifungal activities by broth microdilution method. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) and trolox equivalent antioxidant capacity (TEAC) assays were used to detect the antioxidant activity. The samples were tested spectrophotometrically for their hemolytic properties against human red blood cells. Results: The fractionation of the MeOH extract afforded five known flavonoids including kaempferol (1), quercetin (2), apigenin-7-O-β-D-glucuronopyranoside (3), quercetin 3-O-β-D-galactopyranoside (4) and quercetin 3-O-α-L- rhamnopyranosyl (1 → 6) β-D-glucopyranoside (5). The MeOH extract displayed weak to moderate antimicrobial activities (MIC = 256–2048 μg/ml). Quercetin 3-O-α-L-rhamnopyranosyl (1 → 6) β-D-glucopyranoside (5) and quercetin (2) were respectively the most active compounds against bacteria (MIC = 8–64 μg/ml) and fungi (MIC = 64 – 128 μg/ml). These tested samples also showed high radical-scavenging activities (EC 50 = 5.08 – 70.56 μg/ml) and gallic acid equivalent antioxidant capacities (TEAC = 53.76 – 89.86 μg/ml) when compared with vitamin C (EC 50 = 4.72 μg/ml). The MeOH extract and compounds 2–5 were non-toxic to human red blood cells indicating their high selectivity to be used as antimicrobial and antioxidant drugs. Conclusion: The MeOH extract of O. spinosa as well as compounds 2 – 5 could be a potential source of natural antimicrobial and antioxidant products. Keywords: Oncoba spinosa, Salicaceae, Flavonoids, Antibacterial, Antifungal, Antioxidant Background Infectious diseases are among the main cause of morbid- ity and mortality worldwide, with HIV, tuberculosis and malaria being the most involved. Despite the progress made in the understanding of microorganisms and their control in industrialized nations, incidents due to drug resistant microorganisms and the emergence of hitherto unknown disease-causing microbes, pose enormous pub- lic health concerns [1]. Furthermore, the development of synthetic drugs has slowed down as a result of drug re- sistance [2]. Consequently, this has created a new renewed interest in the search for new drugs in order to combat resistance. The need for new, effective and af- fordable drugs to treat microbial diseases in the develop- ing world is one of the major issues facing global health today. Plants have been used as a source of new medi- cinal compounds throughout history and continue to serve as the basis for many of the pharmaceuticals used today [3]. In recent decades, many studies have been carried out on different plant species to discover com- pounds of possible interest for medicinal application against oxidative stress, fungal and bacterial infections. * Correspondence: jtamokou@yahoo.fr 2 Laboratory of Microbiology and Antimicrobial Substances, Biochemistry Department, Faculty of Science, University of Dschang, PO Box 67, Dschang, Cameroon Full list of author information is available at the end of the article © 2015 Djouossi et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Djouossi et al. BMC Complementary and Alternative Medicine (2015) 15:134 DOI 10.1186/s12906-015-0660-1