Antibacterial activity and mechanism of chitosan with ultra high molecular weight

Chitosan with different degree of deacetylation (DD) and ultra high molecular weight (MW >106) was prepared from β-chitin by mild deacetylation. The effects of DD of chitosan and pH value of its solution/suspension on its antibacterial activity were investigated. The results showed that the optimal pH value was 6.0 for the highest bactericidal activity. The antibacterial activity against Escherichia coli and Staphylococcus aureus of chitosan solution at pH 6.0 enhanced as the DD of chitosan increased. Same as chitosan with low MW, the antibacterial activity of chitosan with high MW in acidic solution was also due to the amino protonation and subsequently cationic formation. Its ultra long molecular chain was propitious to coat and bind the E. coli and S. aureus, and highly enhanced its antibacterial activity. E. coli and S. aureus were at first restrained and then killed by chitosan and the cells were ruptured and decomposed gradually.