Exopolysaccharides as Antimicrobial Agents: Mechanism and Spectrum of Activity

Abstract

Exopolysaccharides (EPSs) are metabolites synthesized and excreted by a variety of microorganisms, including lactic acid bacteria (LAB). EPS serve several biological functions such as interactions between bacteria and their environments, protection against hostile conditions including dehydration, the alleviation of the action of toxic compounds (bile salts, hydrolyzing enzymes, lysozyme, gastric, and pancreatic enzymes, metal ions, antibiotics), and stresses (changing pH, osmolarity), and evasion of the immune response and phage attack. Bacterial EPSs are considered valuable by the food, pharmaceutical, and nutraceutical industries, owing to their health-promoting benefits and rheological impacts. Numerous studies have reported the unusual antimicrobial activities of various EPS against a wide variety of pathogenic microbes (bacteria, virus, and fungi). This review aims to provide a comprehensive examination of the in vitro and in vivo antimicrobial activities of different EPSs, mainly against foodborne bacterial, fungal, and viral pathogens. The mechanism of EPS action against these pathogens as well as the methods used to measure antimicrobial activities are critically reviewed.

Keywords: antibacterial; antifungal; antiviral; biopolymers; biopreservative.

FIGURE 1

Illustration of the potential EPS-cell wall interactions of Gram-negative (A) and Gram-positive (B) responsible for the antibacterial effects of EPSs.

FIGURE 2

Schematic representation of different potential antiviral activities of LAB-derived EPSs including; (1) Prevention of the viral infection through direct binding of viral particles; (2) Obstruction via shielding or masking virus pattern recognition receptor (PRRs) sites; (3) and (4) Stimulation of the immune response in mucosal epithelial and dendritic cells (DC) through their PRRs, resulting in induction of various cytokine production which consequently could modulate antiviral effects by activation of CD+ T lymphocyte differentiation into cytotoxic T lymphocytes; induction of macrophages, stimulation of antiviral activity via phagocytes by activation of Th1, induction of B cell proliferation and viral neutralization activity via secretion of antibodies.