Saponins as agents preventing infection caused by common waterborne pathogens

Waterborne diseases are the leading cause of death globally estimated to result in more than 3.4 million deaths and approximately 4 billion cases of diarrhea worldwide annually according to the World Health Organization (WHO). The United Nations estimates that 4000 children die each day as a result of water-related disease caused by organisms that reside in water sources contaminated by raw sewage. Natural compounds from plants have been the source of multiple drugs. Saponins are a diverse group of glycosides that are widely distributed within the plant kingdom and have an equally broad range of biological properties. Saponin-rich extracts may offer a new microbiocide for the prevention of diarrheal disease caused by enteric viruses and bacteria. In this study, we characterized the antiviral and antibacterial activity of aqueous extracts from Tribulus terrestris, Yucca schidigera and Quillaja saponaria, all of which contain saponins in the range of 45% to 90%. The saponin-containing extracts were examined for their in vitro antiviral activity against two viruses, rhesus rotavirus (RRV) and reovirus serotype 3 (ST3) strain Dearing (MRV-3DE). Saponins were added during the infection, prior and post infection to characterize the antiviral activity. We found that pre-treatment or post treatment of cells alone was not sufficient to block virus infection and subsequent replication. Cotreatment with either saponin containing extracts was able to reduce both rhesus rotavirus and reovirus infectivity. Saponin-containing extracts from Tribulus terrestris demonstrated a more robust activity, about 93 % inhibition against reovirus and 90% inhibition against rhesus rotavirus. These results demonstrate that Tribulus terrestris has antiviral activity that may prove active in vivo. The antibacterial activity of each of the saponin extracts was examined against following water and foodborne pathogens: E. coli 0157:H7, Yersinia enterocolitica, Listeria monocytogenes, two strains of Salmonella enterica subsp. enterica serovar Typhimurium, Shigella flexneri and Vibrio cholerae. Each of the saponin extracts tested in the study did not have growth inhibitory activity against bacterial strains tested.;Next we wanted to examine the ability of each of the saponin extracts to inhibit adhesion and invasion of pathogenic bacteria on cultured HeLa cells. Cellular adhesion and invasion are important events in initiating disease. In fact, a cellular adhesion of bacteria is a first step in pathogenesis. Therefore, prevention of adhesion with broad spectrum inhibitor is an attractive target for designing microbiocide in the prevention of infection. To explore this question, saponin extracts were added simultaneous with or before infection with pathogenic bacteria used in the study to test for their effectiveness in cotreatment and pretreatment assays. The natural saponin extract had not significantly reduced adhesion of individual bacteria to HeLa cells, while invasion was reduced with natural saponin extracts with Y. schidigera saponin extract having the strongest effect.;Next, this study explores a possible mechanism of antimicrobial activity of saponin extracts. Numerous biological properties of saponins have been ascribed to their action on membranes and building on previous findings that certain saponin molecules have affinity for membrane cholesterol, cholesterol assays was applied to see if saponin extracts used in the study can affect this parameter of cellular membrane. The cholesterol assay results suggest that pretreatment of cells with either Y. schidigera or Q. saponaria can modulate cellular membrane cholesterol levels. Also, some saponin molecules have been found to have varying effects on membrane ion channels to either open or block various membrane ion channels. To examine if saponin extract can modulate activity of Ca2+ ion channel, calcium assays was applied. The treatment of cells for 6 hours or 24 hours with either saponin extract did not significantly cause increase or reduction in the concentration of Ca2+ ions in comparison to control.