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Antibacterial Mechanisms of Chitosan and Chitosan Oligosaccharide: Similarities and Differences

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In the realm of natural antibacterial agents, chitosan and chitosan oligosaccharide have garnered significant attention due to their remarkable properties and potential applications. Derived from chitin, a natural biopolymer found in the exoskeletons of crustaceans and the cell walls of fungi, both chitosan and chitosan oligosaccharide possess antibacterial capabilities.

Contents hide
1 Introduction to Chitosan and Chitosan Oligosaccharide​
2 Similarities in Antibacterial Mechanisms​
3 Differences in Antibacterial Mechanisms​

Introduction to Chitosan and Chitosan Oligosaccharide​

Chitosan is the deacetylated product of chitin, chemically named β – 1, 4 – 2 – amino – 2 – deoxy – D – glucose. It is a natural cationic polysaccharide with a relatively high molecular weight, typically ranging from 50,000 to over 1 million daltons. Chitosan is insoluble in water but dissolves in acidic pH due to its amino groups. （See Dora Chitosan）

Chitosan oligosaccharide, on the other hand, is obtained by degrading the main chain of chitosan through physical, chemical, or enzymatic methods. It has a low molecular weight, usually ranging from a few hundred to several thousand daltons, and is water – soluble. This characteristic makes it easier to handle and disperse compared to chitosan. (See Dora Chitosan Oligosaccharide)

Similarities in Antibacterial Mechanisms​

Interaction with the Bacterial Cell Membrane
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Both chitosan and chitosan oligosaccharide can interact with the bacterial cell membrane. In an acidic environment, the amino groups in chitosan are protonated, forming – NH3 +, which can bind to the negatively charged components on the surface of the bacterial cell membrane. This interaction can disrupt the normal structure and function of the cell membrane, leading to increased membrane permeability. Similarly, chitosan oligosaccharide, with its positively charged amino groups, can also bind to the negatively charged bacterial cell membrane. This binding can cause changes in the membrane’s fluidity and permeability, interfering with the normal physiological activities of the bacteria, such as the transport of nutrients and the extrusion of metabolic waste.
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Impact on Bacterial Metabolism​
 
Both substances can interfere with bacterial metabolism. By interacting with the cell membrane and potentially penetrating into the cell, they can disrupt the normal metabolic pathways of bacteria. For example, they may interfere with the synthesis of essential macromolecules such as proteins and nucleic acids. Since bacteria rely on these metabolic processes for growth and reproduction, any disruption can inhibit their growth and lead to antibacterial effects.

Differences in Antibacterial Mechanisms​

Mode of Action Based on Molecular Weight​
Molecular weight plays a crucial role in the antibacterial mechanisms of chitosan and chitosan oligosaccharide. High – molecular – weight chitosan mainly acts on the cell surface. Once it binds to the negatively charged bacterial cell membrane, it forms a polymer film on the cell surface. This film can prevent the transport of nutrients into the cell, starve the bacteria, and disrupt their normal physiological activities. In contrast, low – molecular – weight chitosan oligosaccharide has a smaller molecular size, which allows it to penetrate through the cell membrane pores more easily and enter the bacterial cell interior. Once inside, it can directly interact with intracellular components, such as enzymes and nucleic acids, and have a more direct impact on the core metabolic processes of the bacteria.
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Specific Intracellular Targets​
Chitosan, especially in its lower – molecular – weight forms or after being modified, can penetrate into the cell and interact with DNA. It can bind to DNA, inhibiting the transcription process, which is crucial for the synthesis of mRNA and subsequent protein synthesis. By blocking this process, chitosan can effectively inhibit bacterial growth.
 
Chitosan oligosaccharide, while it can also interact with DNA to some extent, has additional effects on enzymes. It can inhibit the activity of certain key enzymes in bacteria, such as β – lactamase and coagulase. These enzymes are involved in important bacterial physiological functions, and by inhibiting their activity, chitosan oligosaccharide can disrupt bacterial metabolism and growth.
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Immune – related Antibacterial Effects​
Chitosan oligosaccharide has an additional antibacterial mechanism related to immune regulation. It can act as an immunomodulator, stimulating the host’s immune system. In the case of plants, for example, chitosan oligosaccharide can induce plants to produce resistance proteins against pathogens, such as chitinase, chitosanase, and β – 1, 3 – glucanase. These enzymes can act synergistically to enhance the plant’s resistance to pathogens. Chitosan, although it has some immunomodulatory effects, does not have such a direct and specific induction of resistance – related enzymes as chitosan oligosaccharide in the context of antibacterial mechanisms.
Comparison Aspect
Interaction with Cell Membrane
Protonated amino groups bind to negatively charged membrane, forming a surface polymer film
Positively charged amino groups bind to membrane, changing membrane fluidity and permeability
Mode of Action Based on Molecular Weight
High – molecular – weight acts on cell surface; low – molecular – weight can penetrate cell
Small molecular size allows easy penetration into cell interior
Specific Intracellular Targets
Binds to DNA, inhibiting transcription
Interacts with DNA and inhibits key enzymes like β – lactamase and coagulase
Immune – related Antibacterial Effects
Some immunomodulatory effects
Can induce production of plant resistance proteins as an immunomodulator

Chitosan and chitosan oligosaccharide share some similarities in their antibacterial mechanisms, such as interacting with the bacterial cell membrane and interfering with metabolism. However, their differences, mainly due to molecular weight and specific intracellular targets, result in distinct antibacterial effects. Understanding these similarities and differences is essential for optimizing their applications in various fields, including food preservation, agriculture, and medicine, where their antibacterial properties can be harnessed to combat harmful bacteria.

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