Antimicrobial activity of Albizia tulearensis, an endemic Fabaceae from Madagascar

The antimicrobial activity of methanolic extract, butanolic and saponosidic fractions of different organs (leaf, seed, stem bark, root bark) from Albizia tulearensis were tested against 14 pathogenic germs including 5 bacteria Gram-positive (Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes), 6 Gram-negative (Clostridium perfringens, Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Yersinia entericolitica) and 3 yeasts (Candida albicans, Candida tropicalis, Cryptococcus neoformans) using disc diffusion and microdilution methods. At the concentration of 1 mg/disc, the methanolic extracts and fractions of seeds, stem and root bark exhibited selective antimicrobial activity with Inhibition Zone Diameters ranking from 8.67 to 16.5 mm. When using microdilution method, all the methanolic extracts and fractions displayed higher antimicrobial activities while saponosidic fractions were by far the most efficient. Saponosides from leaves (Lsap), seeds (Ssap), stem bark (Bsap) and root bark (Rsap) also exhibited excellent effects with Minimum Inhibitory Concentrations lower than 100 µg/mL against 71.4 %, 21.4 %, 7.14 % and 64.3 % of the germs tested respectively. The most sensitive germs were: S. aureus (4.87 µg/mL) with Rsap and S. pyogenes (9.75 µg/mL) with Lsap in Gram-positive bacteria; E. coli and Y. entericolitica (19.5 µg/mL) with Lsap in Gram-negative bacteria and C. albicans (4.87, 19 and 19.5 µg/mL) with Lsap, Ssap and Rsap respectively in yeasts. The saponosidic fractions had bactericidal and fungicidal effects against the vast majority of the microorganisms tested. The phytochemical screening carried out on plant organs powders revealed the presence of desoxyoses, saponosides, triterpens, unsaturated sterols and phenolic compounds.