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3.3 Antimicrobial Activity
Chitosan is made up of two monomers: glucosamine and N -acetyl glucosamine. The amino
groups of chitosan have cationic properties that are believed to have electrostatic interac-
tions with anionic systems. This property has been found to be quite valuable in using
chitosan as an antibacterial agent [123-125]. It has been proposed that the interaction
between the anionic cell surface of bacteria and the cationic amino group of chitosan weak-
ens the cell membrane of the bacteria. In order to optimize chitosan's antibacterial proper-
ties at physiological pH, the amine group must remain cationic at pH 7.4. This poses a
challenge as chitosan's amine group has a p K a of 6.3, which implies that optimal protona-
tion occurs at an acidic pH (~5.3) [126]. Alteration of the p K a of the amine group is there-
fore a necessary goal to increase the bioactivity of chitosan.
Quaternized chitosan, which has quaternary amino groups introduced into the chitosan
chain, is both a facile and effective method to render it soluble in water. Moreover, quater-
nized chitosan has cationic activity, bioadhesive properties, permeation enhancing effects,
and high efficacy against bacteria and fungi even under neutral conditions [127].