In vitro antibacterial activity of roselle calyx and protocatechuic acid

The in vitro inhibitory effect of roselle calyx and protocatechuic acid, a compound derived from roselle calyx, on the growth of methicillin-resistant Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii was studied. The data from inhibition zone and minimum inhibitory concentration (MIC) values showed that both roselle calyx extract and protocatechuic acid inhibited effectively the growth of all test bacterial pathogens, the antibacterial activity of protocatechuic acid being significantly greater than roselle calyx (p < 0.05). Furthermore, heat treatment did not affect the antibacterial activity of roselle calyx and protocatechuic acid against all test pathogens. The time-kill data from protocatechuic acid showed this agent provided concentration dependent antibacterial activities in broth and human plasma (p < 0.05); however, protocatechuic acid showed less inhibitory activity in human plasma than in broth (p < 0.05). These agents based on their lower MIC values, heat tolerance and concentration dependent antibacterial activity may be useful in clinical infection prevention or therapy.