Antibacterial action of chitosan and carboxymethylated chitosan

A series of chitosan with different molecular weights obtained by gamma -ir radiation depolymerization and another series of deacetylated chitosan were synthesized. Several N,O-carboxymethylated chitosan and O-carboxymethylate d chitosan were also produced. The above samples were characterized by Four ier transform infrared spectroscopy (FTIR). Their antibacterial activities against E. coli were explored by the optical density method. The antibacter ial activity of chitosan is influenced by its molecular weight, degree of d eacetylation, concentration in solution, and pH of the medium. Antibacteria l activities were also found to be increased in the order of N,O-carboxymet hylated 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 micros cope. The antibacterial activity of chitosan oligomers seems to be caused m ainly by the inhibition of the transcription from DNA. (C) 2000 John Wiley & Sons, Inc.