Antibacterial action of chitosan and carboxymethylated chitosan

TLDR

The authors synthesized γ‑irradiation‑depolymerized chitosan of varying molecular weights, deacetylated and carboxymethylated derivatives, characterized them by FTIR, tested antibacterial activity against *E. coli* via optical density, and visualized FITC‑labeled oligomer uptake by confocal microscopy. Antibacterial efficacy depended on molecular weight, degree of deacetylation, concentration, and pH, with N,O‑carboxymethylated chitosan showing the strongest activity, followed by chitosan and O‑carboxymethylated chitosan, likely due to inhibition of bacterial DNA transcription.

Abstract

A series of chitosan with different molecular weights obtained by γ-irradiation depolymerization and another series of deacetylated chitosan were synthesized. Several N,O-carboxymethylated chitosan and O-carboxymethylated chitosan were also produced. The above samples were characterized by Fourier transform infrared spectroscopy (FTIR). Their antibacterial activities against E. coli were explored by the optical density method. The antibacterial activity of chitosan is influenced by its molecular weight, degree of deacetylation, concentration in solution, and pH of the medium. Antibacterial activities were also found to be increased in the order of N,O-carboxymethylated chitosan, chitosan, and O-carboxymethylated chitosan. Fluorescence of the FITC (fluorescein isothiocyanate)-labeled chitosan oligomers at the inside of the E. coli cell was observed by a confocal laser scanning microscope. The antibacterial activity of chitosan oligomers seems to be caused mainly by the inhibition of the transcription from DNA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1324–1335, 2001