This work aimed at assessing the antimicrobial activity of Albizia bernieri seed extracts. Methanol extract (SME), alkaloids extracted under basic (Alk1) and acidic (Alk2) conditions, polar saponosides (Sap1) and less polar saponosides (Sap2) obtained by n-butanol fractionation were used. Their activities were tested against 9 pathogenic germs including 4 Gram (+) bacteria, 5 Gram (-) bacteria and 1 yeast using disc diffusion and microdilution methods. Regardless the method used to assess the antimicrobial activity, all extracts were efficient but their effects depended upon the germs tested. They all displayed a broad spectrum activity. Alkaloids were by far the most efficient with an excellent effect (Minimum Inhibitory Concentration or MIC<100µg/ml) against all germs tested. Streptococcus pneumoniae, Streptococcus pyogenes, Clostridium perfringens and Candida albicans were the most sensitive with MICs less than 10 µg/ml. SME and Sap 2 had moderate or low effects (MIC between 100 and 1000 µg/ml) and Sap1 was the less efficient (MIC ≥1000 µg/ml). All the extracts exerted bactericidal or fungicidal action on all sensitive germs. These preliminary results revealed antimicrobial activity of Albizia bernieri seeds that could be used to treat different infectious diseases and might lead to the development of pharmaceutical agents.

Investigations on the phytotoxicity of Albizia species were conducted under laboratory conditions in order to assess their possible use in the control of weeds and invasive plants. The effects of seed methanolic extracts obtained from A. androyensis, A. bernieri, A. divaricata, A. greveana, A. masikororum and A. viridis, all endemic of Madagascar were evaluated against seed germination and early seedling development of vegetables (Phaseolus vulgaris, Pisum sativum, Petroselinum crispum, Brassica sp., Cucumis sp., Allium cepa, Zea maÿs and Oryza sativa). The effects of these extracts on seed germination of weeds (Eragrostis pilosa, and Panicum subalbidum) and invasive plants (Acacia dealbata, Cassia rotundifolia and Pinus kesyia) were also studied. Globally, all the extracts (1 mg/mL) inhibited the seed germination of all the test plants. However, the inhibitory effect varied according to both the Albizia extract and the target plants. Inhibition rates could reach 100%. The extracts (0.45 to 7 mg/mL) also significantly (p<0.05) reduced the length of both epicotyl and hypocotyl and the effects were generally in a dose dependent manner. At the same concentration (7.2 mg/mL) with some extracts, the inhibitory effect was as high as glyphosate, a weed-killer widely used in agriculture. At low concentrations (0.45-0.9 mg/mL) a high stimulatory effect of up to 200% was observed with some extracts. Overall, the results obtained supported the probable involvement of seed secondary metabolites in the allelopathic interactions of Albizia species with other plants and could be exploitable in the control of undesirable plants.

In this study, we report for the first time the presence of alkaloids belonging to β-carboline type in the pods of the endemic Albizia polyphylla from Madagascar. Three major alkaloids were isolated and structurally identified as: 1-methyl-β-carboline, (+)-(R)-1-methyl-1,2,3,4-tetrahydro-β-carboline and (-)-(S)-1,2-dimethyl-1,2,3,4-tetrahydro-β-carboline.

The aim of this study was to assess the antibacterial potential of Albizia mahalao, a Madagascar Fabaceae. Leaf methanolic extracts (LME), root bark methanolic extract (RME), stem bark methanolic extract (SME), and alkaloids extracted from leaves under basic and acidic conditions were used. All the methanol extracts contained alkaloids and saponins. The antimicrobial activity was tested against many bacteria spp. including; Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens, Enterobacter aerogenes, Salmonella enterica, Shigella flexneri, and Vibrio fischeri, using the Disc diffusion and the Microdilution assays. With the exception of the SME which is inactive, the other extracts exhibited broad spectrum potential against all the tested bacteria. The alkaloids are efficient against nearly all the bacteria under both of the basic and acidic conditions, with an inhibition zone diameter (IZ) of >17 mm, and minimum inhibitory concentration (MIC) of <100 µg/ ml. RME is the least efficient (IZ ≤ 10 mm, and 100< MIC < 1000 µg/ ml). S. enterica is the most sensitive bacterium (IZ= 23 mm, and MIC= 47 µg/ ml), whereas, Staph. aureus (IZ= 10 mm, and MIC >12000 µg/ ml) is the more resistant species. The majority of the extracts expressed bactericidal potency against the tested bacterial spp. Current results revealed the antibacterial potential of the Albizia mahalao leaves and root bark extracts thus could be used to treat infectious diseases.

Seeds of Crotalaria cleomifolia (Fabaceae) are consumed in Madagascar in preparation of popular beverages. The investigation of extracts from the seeds of this species revealed the presence of high amounts of alkaloids from which two pyrrolizidine-derived alkaloids were isolated. One of them was fully characterized by spectroscopic and spectrometric methods, which was found to be usaramine. Owing to the high toxicity of these alkaloids, issuing a strong warning among populations consuming the seeds of Crotalaria cleomifolia must be considered.