Structural Characterization and Antimicrobial Activity of Chitosan (CS-40)/Nisin Complexes

A complex of chitosan (CS-40) and nisin (CS-40/nisin) was prepared and characterized with Fourier transform infrared spectroscopy and thermal analysis (thermogravimetry, differential thermogravimetry, and differential scanning calorimetry). The results show that the complex formed mainly by electrostatic interaction between the protonated amino group in CS-40 backbone with the carboxylate ion of nisin. Minimum inhibitory concentrations (MICs) were evaluated against Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, and Bacillus stearothermophilus), Gram-negative bacteria (Escherichia coli, Salmonella enteritidis, and Proteus vulgaris), and fungi (Fusarium oxysporum). The results show that the CS-40/nisin solution did inhibit or even more strongly inhibited the growth of all the tested microorganisms, whereas CS-40 did not inhibit the growth of F. oxysporum and nisin did not inhibit the growth of Gram-negative bacteria (E. coli, S. enteritidis, and P. vulgaris). The relative inhibition times of CS-40/nisin solutions with different concentrations and ratios of CS-40 and nisin were also investigated against the seven microorganisms. The results showed that CS-40/nisin solutions with CS-40/nisin concentration ratios of 0.05/0.005, 0.05/0.0025, 0.05/0.00125, and 0.025/0.0001% had higher antimicrobial activity against all tested bacteria and fungi. The relationship between complex formation and antimicrobial activity is discussed. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3702-3707, 2010