Antibacterial spectrum of plant polyphenols and extracts depending upon hydroxyphenyl structure

The relationship between the structure and antibacterial activity of 22 polyphenols was analyzed by using minimum inhibitory concentration (MIC) as a criterion against 26 species of bacteria which can grow in Mueller-Hinton medium. There was no clear correlation between Gram-staining and bacterial susceptibility to polyphenols, and the extent of the susceptibility was approximately dependent on the species of bacteria. In the same Gram-negative bacteria, the antibacterial activity of the polyphenols against Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio vulnificus was comparatively strong. On the other hand, the activity against 11 species of the Enterobacteriaceae was comparatively weak, and the activity against six species of aerobic bacteria causing plant disease was moderate. Polyphenols having pyrogallol groups showed strong antibacterial activity, and those with catechol and resorcinol rings showed lower activity. The structure-activity relationship was extended to 26 polyphenol-rich plant extracts which could have potent antibacterial activity suitable for commercial use.