Antibacterial activity and a membrane damage mechanism of Lachnum YM30 melanin against Vibrio parahaemolyticus and Staphylococcus aureus

This study aimed to investigate the antibacterial activity of Lachnum YM30 intracellular melanin (LIM). The dilution method was used to measure the MIC and MBC of Gram-negative bacteria Escherichia coli, Salmonella typhi, Vibrio parahaemolyticus and Gram-positive bacteria Listeria monocytogenes, Bacillus megaterium, Staphylococcus aureus. MIC values for each bacterial strain were 0.4, 2.4, 0.2, 0.6, 0.8, 0.3 mg/mL, and the MBC values were 0.4, 3.2, 0.3, 0.8, 0.8, 0.4 mg/mL, respectively. Bacteriostasis of LIM against S. aureus (G(+)) and V. parahaemolyticus (G(-)) was further revealed by SEM observation, testing integrity of cell membrane, NPN uptake and membrane potential. MTT experiment was used to estimate the cell cytotoxicity of LIM. The results showed that LIM significantly damaged the integrity of cell membrane, increased the leakage of cell contents, raised the quantity of NPN uptake and reduced the membrane potential. LIM had no obvious cell cytotoxicity at low concentrations. These findings indicated that LIM had antibacterial activity and could be applied as a potential natural bacteriostatic agent in the food or pharmaceutical industry. (C) 2016 Published by Elsevier Ltd.