Chitosan

Chitosan is a natural linear polysaccharide composed of β-(1→4)-linked D-glucosamine and N-acetyl-D-glucosamine units. It is produced by the deacetylation of chitin, the second most abundant natural polysaccharide found in crustacean exoskeletons. The resulting free amino groups at the C-2 position give chitosan its characteristic cationic charge at acidic pH, enabling electrostatic interaction with negatively charged microbial cell membranes — the primary mechanism behind its broad-spectrum antimicrobial activity.

Chitosan's antimicrobial effect is primarily driven by electrostatic disruption of microbial cell membranes. The positively charged amino groups (–NH₃⁺) interact with negatively charged surface components — lipopolysaccharides in Gram-negative bacteria, teichoic acids in Gram-positive bacteria, and phospholipids in fungi — causing membrane permeability changes, leakage of intracellular contents, and cell death. Secondary mechanisms include DNA binding (low MW chitosan inhibits mRNA/protein synthesis), metal chelation (sequesters Fe²⁺, Zn²⁺ essential for microbial growth), and surface film formation (high MW chitosan blocks nutrient/oxygen uptake).