Inhibition of Gallic Acid on the Growth and Biofilm Formation of Escherichia coli and Streptococcus mutans

New strategies for biofilm inhibition are becoming highly necessary because of the concerns to synthetic additives. As gallic acid (GA) is a hydrolysated natural product of tannin in Chinese gall, this research studied the effects of GA on the growth and biofilm formation of bacteria (Escherichia coli [Gram-negative] and Streptococcus mutans [Gram-positive]) under different conditions, such as nutrient levels, temperatures (25 and 37 degrees C) and incubation times (24 and 48h). The minimum antimicrobial concentration of GA against the two pathogenic organisms was determined as 8mg/mL. GA significantly affected the growth curves of both test strains at 25 and 37 degrees C. The nutrient level, temperature, and treatment time influenced the inhibition activity of GA on both growth and biofim formation of tested pathogens. The inhibition effect of GA on biofilm could be due to other factors in addition to the antibacterial effect. Overall, GA was most effective against cultures incubated at 37 degrees C for 24h and at 25 degrees C for 48h in various concentrations of nutrients and in vegetable wash waters, which indicated the potential of GA as emergent sources of biofilm control products. Practical Application This study revealed that gallic acid (GA) had a great potential in being developed as a naturally sourced, nontoxic, and novel inhibitor of bacteria. It is the first time to investigate the inhibition effects of GA on the growth and biofilm formation of bacteria under different nutrient levels (such as vegetable wash waters that simulate the nutrient-deprived environments of wash step in real food industry), temperatures, and incubation times. The study addresses the potential of phytochemicals as emergent naturally sources of biofilm control products.