Antimicrobial activity of extracts from Crotalaria bernieri Baill. (Fabaceae)

This work was designed to study the antimicrobial activity of Crotalaria bernieri Baill. (Fabaceae). Extracts from leaf, root, pod and seed using hexane, ethyl acetate and methanol were tested in vitro for their activity against 17 bacteria, 5 fungi (3 yeasts and 2 molds) using disc diffusion and micro dilution methods. At the concentration of 1 mg/disc, all the extracts exhibited antimicrobial activity depending on the plant part and the extraction method used. The most sensitive germs were Salmonella enteridis, Streptococcus pyogenes and Candida guilliermondii with inhibition zone diameter (IZD) of 11 mm, 15 mm and 13 mm respectively. Most of extracts showed, broad activity spectrum varying from one extract to another. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) of all extracts were recorded. Ten extracts displayed an excellent effect (MIC < 100 µg/ml), 8 a moderate effect (MIC from 100 to 500 µg/ml), 5 a weak effect (MIC from 500 to 1000 µg/ml) and the others were ineffective (MIC > 1000 µg/ml). Leaf methanol extracts were the most efficient and Gram positive bacteria the most sensitive. All extracts had bactericidal (MBC/MIC ≤ 4) or fungicidal action (MFC/MIC ≤ 4) in certain microorganisms and bacteriostatic (MBC/MIC > 4) or fungistatic action (MFC/MIC > 4) in others. Antimicrobial activity might be due to tannins, polyphenols, steroids, triterpenes and flavonoids that were present in most of the plant organs, but alkaloids in leaf and pod and saponosides in root might also be involved. C. bernieri with the effectiveness of all its parts, the variety of its secondary metabolites, the great number of sensitive pathogen microorganisms and its ubiquity make this plant species an interesting source of antimicrobial agents.