Antimicrobial Actions and Applications of Chitosan

Abstract

Chitosan is a naturally originating product that can be applied in many areas due to its biocompatibility, biodegradability, and nontoxic properties. The broad-spectrum antimicrobial activity of chitosan offers great commercial potential for this product. Nevertheless, the antimicrobial activity of chitosan varies, because this activity is associated with its physicochemical characteristics and depends on the type of microorganism. In this review article, the fundamental properties, modes of antimicrobial action, and antimicrobial effects-related factors of chitosan are discussed. We further summarize how microorganisms genetically respond to chitosan. Finally, applications of chitosan-based biomaterials, such as nanoparticles and films, in combination with current clinical antibiotics or antifungal drugs, are also addressed.

Keywords: antimicrobial activity; chitosan; films; nanoparticles; physicochemical characteristics.

Figure 1

Potential antimicrobial actions of chitosan against (A) gram-positive bacteria, (B) gram-negative bacteria, and (C) fungi. Given the negative charges of teichoic acids in gram-positive bacteria, lipopolysaccharide (LPS) in gram-negative bacteria and the phosphorylated mannosyl side in fungi, electrostatic interactions occur between the positively charged chitosan and the cell surface of the microorganism. Furthermore, chitosan chelates the environmental ions and nutrients required for bacterial survival. Low-molecular weight (MW) chitosan and oligo-chitosan might affect DNA/RNA or protein synthesis after passing through the cell wall and cell membrane into the cytoplasm. Additionally, low-MW chitosan and oligo-chitosan inhibit mitochondrial function and ATP production.

Figure 2

Potential signaling cascades and factors required for chitosan tolerance in C. albicans. Mutant library screening has revealed that the Hog1, Cek1/Cek2, Mkc1, Ras1-cAMP, and calcineurin cascades as well as the Ssn3-mediated Sef1 pathway and other factors are involved in chitosan resistance. The roles of these pathways and factors in mediating cell wall integrity might affect mitochondrial function. Furthermore, low-MW chitosan directly represses mitochondrial function, leading to ATP production inhibition.