Antibacterial Activity and Chemical Analyses of the Alkaloidal Fraction of Neltuma laevigata (Humb. & Bonpl. Ex Willd) Britton & Rose Inflorescences

Species of the <i>Neltuma</i> syn <i>Prosopis</i> genus are known for their use in traditional medicine in America, Asia and Africa. The use of the leaves, bark and inflorescences of one species widely distributed in the arid zones of Mexico, <i>Neltuma laevigata</i> (Humb. & Bonpl. Ex Willd) Britton & Rose, has been reported for the treatment of ocular, gastric and skin infections. Its activities have been related to different secondary metabolites, particularly phenylpropanoids and alkaloids. In the present study, the antibacterial activity of the alkaloidal fraction of inflorescences of <i>P. laevigata</i> collected in Zapotitlán Salinas, Puebla, México, against <i>Staphylococcus aureus</i> ATCC 25,923 and <i>Vibrio cholerae</i> CDBB-1159 was studied by Kirby-Baüer and broth microdilution tests, and its activity on plasmatic membranes was later identified using a protein leakage assay and fluorescence microscopy. Subsequently, the alkaloidal fraction was separated via chromatographic methods, and the purified compounds were elucidated using nuclear NMR and HRESIMS analysis. The alkaloidal fraction showed an important antibacterial activity, with a possible effect on the cytoplasmic membrane of the tested strains. Julifloridine, a piperidine alkaloid previously reported in the genus, was identified for the first time in this species.