AUTHOR=Baien Shima Hassan , Seele Jana , Henneck Timo , Freibrodt Christin , Szura György , Moubasher Hani , Nau Roland , Brogden Graham , Mörgelin Matthias , Singh Mahavir , Kietzmann Manfred , von Köckritz-Blickwede Maren , de Buhr Nicole 

TITLE=Antimicrobial and Immunomodulatory Effect of Gum Arabic on Human and Bovine Granulocytes Against Staphylococcus aureus and Escherichia coli

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.03119

DOI=10.3389/fimmu.2019.03119

ISSN=1664-3224

ABSTRACT=<p>Gum arabic (GA) is a traditional herbal medicine from <italic>Acacia Senegal</italic> (L.) Willdenow trees, which consist of a complex mixture of polysaccharides and glycoproteins. It is used in daily applications for several diseases and is considered to protect against bacterial infections. The detailed mechanisms behind these observations are still unclear. In this study, we investigated the direct antibacterial activity of GA water and ethanol extracts against <italic>Staphylococcus</italic> (<italic>S</italic>.) <italic>aureus</italic> or <italic>Escherichia</italic> (<italic>E</italic>.) <italic>coli</italic> and the immunomodulating properties of those extracts on granulocytes as a first line of defense against bacteria. Firstly, the direct antimicrobial effect of GA was tested on three different <italic>S. aureus</italic> strains and two <italic>E. coli</italic> strains. The growth of bacteria was analyzed in the presence of different GA concentrations over time. GA water as well as ethanol extracts showed a significant growth inhibition in a concentration-dependent manner in the case of <italic>S. aureus</italic> Newman, <italic>S. aureus</italic> Rd5, and <italic>E. coli</italic> 25922, but not in the case of <italic>S</italic>. <italic>aureus</italic> USA300 and <italic>E. coli</italic> K1. Transmission electron microscopic analysis confirmed an antibacterial effect of GA on the bacteria. Secondly, the immunomodulatory effect of GA on the antimicrobial activity of bovine or human blood-derived granulocytes was evaluated. Interestingly, water and ethanol extracts enhanced antimicrobial activity of granulocytes by the induction of intracellular ROS production. In line with these data, GA increased the phagocytosis rate of <italic>E. coli</italic>. No effect was seen on neutrophil extracellular trap (NET) formation that mediates killing of extracellular bacteria such as <italic>S. aureus</italic>. In conclusion, we show that GA exhibits a direct antibacterial effect against some <italic>S. aureus</italic> and <italic>E. coli</italic> strains. Furthermore, GA boosts the antimicrobial activities of granulocytes and increases intracellular ROS production, which may lead to more phagocytosis and intracellular killing. These data might explain the described putative antimicrobial activity of GA used in traditional medicine.</p>