Antibacterial activity of various chitosan forms against Xanthomonas axonopodis pv. glycines

In this study, the antibacterial activities of colloidal chitosan, chitosan solution, and chitooligosaccharide solution were evaluated against Xanthomonas axonopodis pv. glycines grown in peptone sucrose broth (PSB) medium. Treatment with colloidal chitosan (0.01, 0.025, and 0.05%) inhibited X. axonopodis pv. glycines growth only until 36 h. Thin-layer chromatography analysis detected some metabolites, consistently with the cell growth pattern. Two chitooligosaccharides (1-3 kDa and 5-10 kDa) dissolved in distilled water and acetic acid did not exhibit antibacterial activity against X. axonopodis pv. glycines at all tested concentrations (0, 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.05%). Compared to the control, the chitosan solution decreased X. axonopodis pv. glycines cell growth by 58.7% and 99.0% at concentrations of 0.015% and 0.02%, respectively, after 3 d of incubation. The chitosan solution exhibited the highest antibacterial activity at pH 6.5. However, the antibacterial activity of chitosan decreased in the presence of NaCl and MgCl₂.