Evaluation of antibacterial activity of compounds isolated from the peel of Newhall navel orange.

Fifteen compounds including one flavanone hesperitin (), two cinnamic acid derivatives as ()-4-hydroxycinnamic acid () and ()-ferulic acid (), eight polymethoxyflavones (PMFs) (-), and four hydroxylated PMFs (-) isolated from orange peel were subjected to antibacterial evaluation. Compounds - exhibited wide-spectrum antibacterial effects against four test strains involving , , subsp. (), and Meticillin-resistant (MRSA) with minimum inhibitory concentrations (MICs) ranging from 0.0312 to 0.125 mg/mL. In contrast, all PMFs showed weak antibacterial activity against these four strains with MICs being equal to or more than 0.125 mg/mL. Hydroxylated PMFs demonstrated better antibacterial effect against relative to PMFs. In addition, the synergistic effect against was obtained when compounds and were combined. Furthermore, the scanning electron microscopy (SEM) results of treated with both compounds and showed shrunken and rough surface morphologies, indicative of the cell membrane damage.