Chitosans with different Degrees of Deacetylation (DDs) or different Molecular Masses (MMs) were prepared. The antibacterial
activities of the prepared chitosans against Staphylococcus aureus ( S. aureus) , Escherichia coli (E. coli) , Bacillus subtilis (B. subtilis) and Pseudomonas
fluorescens (P. fluorescens) were then determined and compared by measuring the MIC ( Minimum Inhibitory Concentration). Results indicate that the antibacterial activities of chitosans with the same DD increase with their MMs ranging from 400 to 800ku, that chitosans with different DDs (68.4%, 75.3%, 83.6% and 93.7%) but approximate MM ( about 430 ku) possess almost the same
antibacterial activity, that chitosan has the highest antibacterial activity at the pH value of about 5.5 to 6. 0, that the growth of S. aureus can be easily inhibited by chitosan, while E. coli is the bacterium that is most difficult to inhibit in the experiment, and that, generally, all tested chitosans have strong antibacterial activity against the four bacteria, which is higher than that of sodium benzoate (C7H5O2Na).