9 - Antimicrobial applications of chitosan

Abstract

This chapter provides information and insights into the effects of chitosan chemistry and interactions with microbial cell walls and on antimicrobial actions. The influence of chemistry, molecular weight (MW), degree of deacetylation (DDA), and functionalization of chitin/chitosan molecules on antimicrobial properties is described. The critical MW for bacterial growth inhibition by chitosan has been shown to be above 10kDa against Gram positive and Gram negative bacteria. With increasing MW of chitosan, antibacterial activity was increased, especially against Escherichia coli (E. coli). However, increases in MW of chitosan over 100kDa have been shown to reduce the antibacterial activity against E. coli, while this trend was not observed against Gram positive bacteria. Chitosan with higher DDA, and thus higher in positive charges, would be expected to have stronger inhibitory effect against both Gram positive and Gram negative bacteria. The understanding of the composition of microbial outermost membranes and the sites of antimicrobial actions are necessary for effective molecular design and/or synthesis of chitin/chitosan derivatives for novel antimicrobial agents. Quaternization of chitin/chitosan by substitution of quaternary ammonium groups is the derivatization process most frequently applied to functionalize chitin/chitosan for use as antimicrobial agents.