Abstract: The relationship between antibacterial activity of chitosans and their chemical structure(DA, degree of acelytation and DP, degree of polymerization) was investigated. MICs(minimum inhibiting concentration) of four different series of 29 different “pure” chitosans whose DA and DP were well characterized against four different bacteria(gram-positive bacterium E. coli K1, gram-negative bacteria Bacillus cereus, Bacillus megaterium and Staphlylococcu aureus) were determined with micro plate reader. The growth and MICs of these 29 chitosans against these bacteria were different for different bacteria. Antibacterial activity of chitosan depended on bacterium itself even though it was independent directly of the gram-positive or gram-negative bacterium. Every growth pattern and MIC against two bacteria(E. coli K1 and Bacillus cereus) were analyzed and compared with their chemical structure(DA and DP). The results show that antibacterial activity(or MIC) of every chitosan was different even against the same bacterium, nd the antibacterial activity of every chitosan against different bacteria was different. The antibacterial activity of a chitosan depended on the chemical structure of the chitosan, the antibacterial activity of the chitosans was increased with decreasing DA of the chitosans when DP of the chitosans was the same, and that antibacterial activity was increased with decreasing DP of the chitosans when DA of the chitosans was the same. These results suggest that static electricity might be the main force of antibacterial activity of a chitosan.

Key words: Chitosan, Antibacterial activity, MIC, Bacterium