Abstract:

The antibacterial activities of chitosan against Pseudomonas aeruginosa (P. aeruginosa), Proteus mirabilis (P. mirabilis) and Escherichia coli (E. coli) were evaluated by optical density method. Meanwhile, bacterial cell surface hydrophilicity and negative charge analysis were investigated to illustrate the relationship between surface characteristics of Gram-negative bacterial cell wall and antibacterial activity of chitosan. To investigate the action mode of chitosan towards Gram-negative bacterial, E. coli was selected to be representative of bacteria. The permeability of the outer membrane was investigated by determining the changes in the fluorescence intensity of cells treated with the fluorescent probe of 1-N-phenylnaphthylamine (NPN). Furthermore, the interaction of chitosan with E. coli was studied by Fourier-transform infrared spectroscopy (FT-IR). Results showed that the Gram-negative bacteria with better hydrophilicity and more negatively charged cell surfaces exhibited greater interaction with chitosan and accordingly chitosan had preferable antibacterial activity against them. Chitosan increased the permeability of outer membrane and ultimately disrupted bacterial cell membranes. This damage was likely caused by the electrostatic interaction between —NH3+ groups of chitosan and carbonyl or phosphoryl groups of phospholipid components of cell membranes.

Key words: chitosan, Gram-negative bacteria, antibacterial activity, mechanism