Precise quantification of the antibacterial activity of chitosan by NB medium neutralizer

Abstract In the present research, nutrient broth (NB) medium was identified to be able to neutralize the antibacterial activity of chitosan and its derivatives. Therefore, an improved test method independent of NB medium was proposed to precisely quantify the antibacterial effectiveness and efficiency of chitosan. The minimum bactericidal concentration (MBC) of chitosan was 60 μg mL-1 against S. aureus and E. coli, and 0.01% (w/v) chitosan could kill 100% of bacteria within 3 min. From another point of view, the neutralizing efficiency of NB could be tripled by adding 25 g L-1 of sodium chloride. Then the neutralizing mechanism of NB medium was ascribed to flocculation between chitosan and protein. Adding extra sodium chloride could significantly reduce the size of floccules, and smaller floccules would lose the ability of binding with bacteria directly, showing higher neutralizing rate on the macro scale.