Abstract:

The optical density (OD) and agar plate methods were employed to measure the antibacterial activities and the MICs of chitosans with different molecular weights against Staphylococcus aureus (St. aureus) and Escherichia coli (E. coli), respectively. The membrane permeabilities of St. aureus and E. coli treated with 50-kD molecular weight chitosan were investigated by determining the relative conductivity and the permeability of outer membrane of E. coli treated with the chitosan by determining the fluorescence with 1-N-phenylnaphthylamine (NPN) as the fluorescent probe. In addition, the effect of the 50-kD molecular weight chitosan on fluorescence spectrum of membrane protein of E. coli was investigated to elucidate the antibacterial mechanism of the chitosan. Results showed that the 50-kD molecular weight chitosan increased the membrane permeability of St. aureus and E. coli and ultimately disrupted the bacterial cell membrane. Also, this chitosan quenched fluorescence activity of tryptophan (Trp) residues, and the quenching action performed in static state, suggesting that the action target of chitosan to bacteria is their membrane.

Key words: chitosan, cell membrane, membrane protein