Abstract: The chitosan microspheres (CMs) were prepared via emulsion chemical cross-linking method. The antibacterial activities of CMs with different concentrations and different diameters against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25992 were investigated, and the inhibition mechanisms were also discussed. The results indicated that the antibacterial activities increased with the increasing of concentration and the decreasing of diameter of CMs. The CMs could inhibit the growth of the bacteria in the initial stage and then promote it when the concentration was lower than 0.7 mg/mL. The CMs exhibited the bactericidal effect completely when the concerntration was higher than 0.7 mg/mL. The minimum inhibitory concentrations and the minimum bactericidal concentrations were 0.8 mg/mL and 1.4 mg/mL respectively for S. aureus and 1.0 mg/mL and 1.8 mg/mL respectively for E. coli. The results showed that CMs could inhibit the growth of the Gram-positive and Gram-negative bacteria effectively, and the Gram-positive bacteria were more sensitive than Gram-negative bacteria. The SEM images showed that the bacteria could adhere to CMs quickly with obviously morphology changing.

Key words: chitosan microspheres, emulsion chemical cross-linking method, antibacterial activities