Antibacterial lectin from Moringa oleifera seeds (WSMoL) has differential action on growth, membrane permeability and protease secretory ability of Gram-positive and Gram-negative pathogens

Abstract The water-soluble lectin from Moringa oleifera seeds (WSMoL) has been reported as an antimicrobial agent against pathogenic and corrosive bacteria. In the present study, we investigated the antibacterial activity of WSMoL against four human pathogenic bacteria as well as its cytotoxicity to human peripheral blood mononuclear cells (PBMCs). Bacteriostatic, bactericidal, and agglutinating effects of WSMoL, along with its damaging effects on membrane integrity and its effect on protease secretion were investigated. WSMoL showed bacteriostatic and bactericidal activities against Enterococcus faecalis , Klebsiella pneumoniae , and Serratia sp. but only had bacteriostatic activity against Micrococcus luteus . The lowest minimal inhibitory and bactericidal concentrations (15.6 and 125 μg/mL, respectively) were detected for E. faecalis ; on the contrary, the bacteriostatic effect was faster for the Gram-negative bacteria ( K. pneumoniae and Serratia sp.). WSMoL promoted agglutination and caused protein leakage from all bacteria. Confocal fluorescence microscopy showed that WSMoL caused a loss of bacterial cell integrity. A significant decrease of extracellular protease activity was detected only for Gram-negative bacteria. WSMoL (50 μg/mL) did not promote PBMCs death. In conclusion, WSMoL showed differential action on the pathogenic Gram-negative and Gram-positive bacteria, affecting membrane permeability and integrity.