Antibacterial activity and mechanism of a laccase-catalyzed chitosan-gallic acid derivative against Escherichia coli and Staphylococcus aureus

In this paper, the antimicrobial activity and mechanism of a laccase-catalyzed chitosan-gallic acid derivative were evaluated. The results showed that compared to the parent chitosan, the derivative could significantly inhibit the growth of Escherichia coli and Staphylococcus aureus, wherein the latter was more sensitive to the derivative than the former. The chitosan-gallic acid derivative could disrupt the cell membrane of E. coli and S. aureus, resulting in leakage of cytoplasm and an increase in relative conductivity. The morphological changes were manifested by the aggregation of bacterial cells and formation of an irregular shape. Agarose gel electrophoresis showed that chitosan derivatives could enter bacterial cells through damaged cell membranes and inhibit DNA synthesis in the nucleus. In addition, the cytotoxicity was significantly reduced by proper modification of chitosan with gallic acid. The above results indicated that there was a great potential for laccase-catalyzed chitosan-gallic acid derivative for use as a food preservative.