Kuwanon G:: an antibacterial agent from the root bark of Morus alba against oral pathogens

Kuwanon G was isolated from the ethyl acetate fraction of methanol extract of Morus alba and its structure was elucidated by C-13-NMR, H-1-NMR and FAB-MS. Antibacterial activity of kuwanon G was investigated by the minimum inhibitory concentration (MIC) test and the viable cell count method. MIC of kuwanon G against Streptococcus mutans causing dental caries was determined to be 8.0 mug/ml. The bactericidal test showed that kuwanon G completely inactivated S. mutans at the concentration 20 mug/ml in 1 min. Kuwanon G also significantly inhibited the growth of other cariogenic bacteria such as Streptococcus sobrinus and Streptococcus sanguis, and Porpyromonas gingivalis causing periodontitis. Transmission electron microscopy (TEM) of kuwanon G treated cells demonstrated remarkable morphological damage of the cell wall and condensation of the cytoplasm. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.