Chitosan and its antimicrobial potential--a critical literature survey - PubMed (original) (raw)

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Chitosan and its antimicrobial potential--a critical literature survey

Dina Raafat et al. Microb Biotechnol. 2009 Mar.

Abstract

Chitosan, an aminopolysaccharide biopolymer, has a unique chemical structure as a linear polycation with a high charge density, reactive hydroxyl and amino groups as well as extensive hydrogen bonding. It displays excellent biocompatibility, physical stability and processability. The term 'chitosan' describes a heterogeneous group of polymers combining a group of physicochemical and biological characteristics, which allow for a wide scope of applications that are both fascinating and as yet uncharted. The increased awareness of the potentials and industrial value of this biopolymer lead to its utilization in many applications of technical interest, and increasingly in the biomedical arena. Although not primarily used as an antimicrobial agent, its utility as an ingredient in both food and pharmaceutical formulations lately gained more interest, when a scientific understanding of at least some of the pharmacological activities of this versatile carbohydrate began to evolve. However, understanding the various factors that affect its antimicrobial activity has become a key issue for a better usage and a more efficient optimization of chitosan formulations. Moreover, the use of chitosan in antimicrobial systems should be based on sufficient knowledge of the complex mechanisms of its antimicrobial mode of action, which in turn would help to arrive at an appreciation of its entire antimicrobial potential.

© 2009 The Authors. Journal compilation © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd.

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Figures

Figure 1

Figure 1

Chemical structure of chitosan, its production from chitin and the specificity of chitosanases. Chitosan is a (1→4)‐linked 2‐amino‐2‐deoxy‐_β_‐

d

‐glucan, prepared from chitin through alkaline hydrolysis of the _N_‐acetyl groups. Upon further hydrolysis, for example, with the help of chitosanases (indicated by black arrows), low‐MW oligosaccharides are produced.

Figure 2

Figure 2

The staphylococcal cell envelope. The staphylococcal cell wall is composed of multilayers of glycan strands of alternating _N_‐acetylglucosamine (Glc_N_Ac) and _N_‐acetylmuramyl‐pentapeptide (Mur_N_Ac‐PP), cross‐linked by pentaglycine side‐chains. For clarity, only one layer of peptidoglycan is depicted here. Teichoic acids, polyanionic surface polymers extending through the peptidoglycan layer, contribute to the negative charge of the cell wall. The cytoplasmic membrane is a selectively permeable membrane lying internal to the cell wall.

Figure 3

Figure 3

Detailed structure of a chitosan molecule. Shown is an enlarged portion of a chitosan molecule, with relevant dimensions. For a chitosan molecule of a MW of 240 kDa and a DD of 87%, an average chain would consist of around 1400 units, with an average length of about 700 nm.

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