Effect of MW and concentration of chitosan on antibacterial activity of Escherichia coli

Different molecular weight (MW) chitosans (5.5×104 to 15.5×104 Da) with the same degree of deacetylation (80%±0.29), were obtained by the method of acetic acid hydrolysis. The effect of antimicrobial activities of chitosan and acetic acid against Escherichia coli were investigated. All of the chitosan samples with MW from 5.5×104 to 15.5×104 Da had antimicrobial activities at the concentrations higher than 200 ppm. The growth of E. coli was promoted at concentration lower than 200 ppm. The antibacterial activity of chitosan had relationship to the MW at the concentration range from 50 to 100 ppm. The antibacterial activity of low MW chitosan is higher than that of the high MW samples. But the chitosan sample with the middle MW (9.0×104 Da) could promote the growth of bacteria. In the different stages of cultivation, the earlier chitosan was added the greater effect it did. And the mechanism of antibacterial activity was that E. coli was flocculated.