- Polysaccharides have emerged as an important class of natural compounds with antimicrobial activity, offering potential alternatives or adjuncts to synthetic antibiotics. Their antimicrobial effects are broad, targeting bacteria, fungi, and even some protozoa, and arise from both direct mechanisms—such as disrupting microbial cell structures—and indirect mechanisms, including immune system activation and inhibition of microbial colonization. Their activity depends strongly on structural features such as monosaccharide composition, molecular weight, degree of branching, and presence of functional groups (e.g., amino, hydroxyl, sulfate).
- One of the most widely studied antimicrobial polysaccharides is chitosan, obtained by deacetylation of chitin from crustaceans, fungi, and insects. Its antimicrobial action is primarily attributed to its positively charged amino groups, which interact with negatively charged bacterial cell membranes. This electrostatic interaction increases membrane permeability, causes leakage of intracellular contents, and ultimately leads to microbial death. Chitosan also inhibits biofilm formation, an important factor in bacterial resistance and pathogenicity. Its effectiveness has been demonstrated against a wide range of bacteria, including Escherichia coli, Staphylococcus aureus, Salmonella, and Listeria monocytogenes.
- Other plant-derived polysaccharides, such as pectins, gums, and mucilages, also exhibit antimicrobial properties. Pectins rich in galacturonic acid residues can bind to microbial surfaces, reducing adhesion and colonization, while gums such as gum arabic and xanthan gum may form protective barriers that prevent microbial proliferation. In addition, some plant polysaccharides exert indirect antimicrobial effects by promoting the growth of beneficial gut microbiota (prebiotic activity), thereby inhibiting pathogenic bacteria through competitive exclusion.
- Fungal polysaccharides, particularly β-glucans, are not directly bactericidal but contribute to antimicrobial defense by stimulating the host immune system. They activate macrophages, neutrophils, and natural killer (NK) cells, leading to enhanced phagocytosis and production of antimicrobial peptides. This immune-boosting property is especially important in host defense against fungal pathogens and bacterial infections. Similarly, bacterial exopolysaccharides like dextran and levan can interfere with microbial adhesion, while modified forms may display enhanced antimicrobial action.
- The mechanism of antimicrobial action of polysaccharides varies depending on their source and structure. They may:
- Disrupt microbial membranes through electrostatic or hydrophobic interactions (e.g., chitosan).
- Inhibit biofilm formation and quorum sensing, reducing microbial virulence.
- Chelate essential trace metals (e.g., iron, zinc), depriving microbes of nutrients needed for growth.
- Enhance host immunity, indirectly strengthening resistance to infections.
- From an application standpoint, antimicrobial polysaccharides are being explored in medicine, food preservation, agriculture, and biomaterials. In medicine, chitosan and alginate-based wound dressings not only accelerate healing but also prevent infection. In food science, edible polysaccharide coatings and films can inhibit microbial spoilage and extend shelf life. In agriculture, polysaccharide formulations provide eco-friendly alternatives to chemical pesticides, protecting plants against bacterial and fungal pathogens. Furthermore, in drug delivery, polysaccharides serve as antimicrobial carriers that improve drug stability and targeted release.
