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 °C) and incubation times (24 and 48 h). The minimum antimicrobial concentration of GA against the two pathogenic organisms was determined as 8 mg/mL. GA significantly affected the growth curves of both test strains at 25 and 37 °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 °C for 24 h and at 25 °C for 48 h in various concentrations of nutrients and in vegetable wash waters, which indicated the potential of GA as emergent sources of biofilm control products.