Bioactivities of Chitosan and Its Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 139

12

P. gingivalis
P. intermedia
A. actinomycetemcomitans

*** # # # 10

8

6

**

4

2

0

HTCC (LA)
solution

CS (LA) solution HTCC (H 2 O)

solution

Figure 3.12
Inhibition zone diameter for different samples.

The effect of MW on antifungal activity was investigated [131]. Experiments were con-
ducted to test their antifungal activities against Botrytis cinerea Pers. ( B. cinerea Pers.) and
Colletotrichum lagenarium (Pass) Ell.et halst ( C. lagenarium (Pass) Ell.et halst). The results indi-
cate that quaternized chitosan derivatives have stronger antifungal activities than chitosan.
Furthermore, quaternized chitosan derivatives with high MW are shown to have even
stronger antifungal activities than those with low MW.

3.3.3 Mechanism of inhibition

3.3.3.1 Antibacterium Mechanism of Chitosan and HTCC

To date, the mechanism of inhibition of chitosan on bacteria is not clear. One possibility
is that, due to the interaction between the two charges, the bacterial cell wall breaks, lead-
ing to cytoplasmic leakage, which eventually causes cell death [132-134]. In addition,
stacking of chitosan molecules over the microbial cell surface may block the transport of
nutrients [135] or binding to DNA, thus inhibiting transcription or permeabilization of
the microbial cell wall/membrane. Helander et al. [133] showed that the binding of chito-
san to the outer membrane of a Gram-negative bacteria resulted in a vesicular structure,
causing disruption and extensive alteration to the outer membrane surface, resulting in
the loss of its barrier properties.
No et al. [136] found that the antibacterial activities of chitosan are strain dependent.
Other investigators have shown that an increase in the MW and degree of deacetylation
(DD) of chitosan enhances antibacterial activity [137]. A higher DQ of HTCC should
enhance antibacterial activity. In the experiments, HTCC exerted more potent antibacterial
activities than chitosan in the same solution against P. intermedia , A. actinomycetemcomitans ,
and S. mutans. This was probably due to the introduction of quaternary ammonium salts
onto the chitosan backbone, which enhanced the water solubility of chitosan and increased
the antimicrobial activity of HTCC over the entire pH range.