Antibacterial activity of chitosans with different degrees of deacetylation and viscosities

Summary Antibacterial activities of six acid‐soluble [two degrees of deacetylation (DD) × three viscosities] and two water‐soluble chitosans (two DD with similar viscosities) were examined against eight gram‐negative ( Pseudomonas fluorescens , Proteus vulgaris , Erwinia carotovora , Serratia marcescens , Escherichia coli, Vibrio parahaemolyticus , V. vulnificus , and Salmonella Typhimurium) and six gram‐positive bacteria ( Listeria monocytogenes , Staphylococcus aureus , Bacillus subtilis , B. cereus , Lactobacillus curvatus , and L. plantarum ). Antibacterial activities of chitosans differed depending on the chitosan types and bacteria tested. Water‐soluble chitosans inhibited bacterial growth by one to eight log cycles at 0.1% concentration; however, the effects were much lesser than those observed with 0.05% acid‐soluble chitosans. Minimum inhibitory concentration (MIC) values (0.03% to above 0.1%) of acid‐soluble chitosans were much lower than those (0.05% to above 0.8%) of water‐soluble chitosans. Based on MIC values, the acid‐soluble chitosan with 99% DD and lower viscosity (17.9 mPa s) was most effective in inhibiting bacteria growth among eight chitosans tested.