Comparative metabolomic study of twelve Acacia species by UHPLC-q-tof-ESI-MS coupled with chemometrics in correlation with antibacterial activity

Genus Acacia comprises around 1500 species. They are widely used to treat inflammation as well as bacterial and fungal infections as they are enriched in phytochemicals, especially phenolics. The aim of this study was to evaluate the antibacterial activity of leaves' methanolic extracts of twelve Acacia species growing in Egypt against Vibrio parahaemolyticus, Salmonella enterica, Listeria monocytogens, Klebsiella pnemoniae, Bacillus aquimaris, Bacillus subtilis, and Escherichia coli. These species are Acacia nilotica (wild and cultivated), Acacia seyal, Acacia auriculiformis, Acacia saligna, Acacia xanthophloea, Acacia tortilis subsp. raddiana (Gabal Elba and Aswan), Acacia tortilis, Acacia laeta (wild and cultivated), and Acacia albida. Furthermore, to study the metabolomic composition and variation among these species using ultra-high-performance liquid chromatography-electrospray ionization quadrupole time of flight mass spectrometry (UHPLC-q-tof-ESI-MS) coupled with multivariate statistical analysis and correlate it to the antibacterial potential. Results showed that Acacia nilotica (AN) has superior antibacterial activity over the other species. In addition, it exhibited a distinct segregation in Principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA). Full profiling of AN using UHPLC-ESI-q-tof-MS revealed 42 phenolics mainly catechins. It was further subjected to bio-guided fractionation and revealed the presence of methyl gallic acid, gallic acid, catechin gallate, and digallate isomers in its most bioactive fraction. These compounds were identical to the compounds annotated as VIPs and were responsible for the segregation of AN in both PCA and PLS-DA analyses. Hence, this study sheds light on the use of chemometrics as an early tool for the detection of bioactive compounds.