Antibacterial Activity of Shrimp Chitosan against Escherichia coli

The effects of cell age, reaction temperature, pH value, and salts on the inhibitory activity of shrimp chitosan (98% deacetylated) against Escherichia coli were investigated. The age of a bacterial culture affected its susceptibility to chitosan, with cells in the late exponential phase being most sensitive to chitosan. Higher temperature (25 and 37°C) and acidic pH increased the bactericidal effects of chitosan. Sodium ions (100 mM Na⁺) might complex with chitosan and accordingly reduce chitosan's activity against E. coli. Divalent cations at concentrations of 10 and 25 mM reduced the antibacterial activity of chitosan, in the order of Ba²⁺ > Ca²⁺ > Mg²⁺. Chitosan also caused leakage of glucose and lactate dehydrogenase from E. coli cells. These data support the hypothesis that the mechanism of chitosan antibacterial action involves a cross-linkage between the polycations of chitosan and the anions on the bacterial surface that changes the membrane permeability.