Assay of Bactericidal Features of Natural Polyphenols Using a Model Test Culture of Bacillus subtilis

This study concerns the antimicrobial effects of various natural polyphenols, namely resveratrol, dihydroquercetin, dihydromyricetin, baykalein, chrysin, rutin, and daidzein, using a model test culture of Bacillus subtilis VKPM B-4419 isolated from children’s dairy products. Pretesting of polyphenols on pathogenic microorganisms, including the species Staphylococcus aureus and Escherichia coli, and fungi of Candida albicans and Aspergillus niger, showed that four of the eight compounds tested, namely daidzein, resveratrol, dihydroquercetin, and dihydroquercetin, inhibited the growth of Gram-positive S. aureus and Gram-negative E. coli. Daidzein and resveratrol at a concentration of 15 mM proved most successful against bacterial pathogens, while dihydroquercetin blocked the growth of S. aureus at a concentration of 30 mM and dihydromyricetin inhibited the growth of E. coli at 150 mM. None of the polyphenols studied inhibited the growth of the fungal pathogens. Study of the impact of natural polyphenols on the growth and viability of the model nonpathogenic Gram-positive strain of B. subtilis VKPM B-4419 confirmed that daidzein and resveratrol inhibited its growth by 45–56% compared to that in the control. It was comparable to the action of the antibiotics vancomycin and chloramphenicol. Daidzein and resveratrol formed growth-free zones upon testing with the method of diffusion into agar. Daidzein inhibited bacterial metabolism at the stationary growth stage by 26%, while the combined effect of daidzein and chloramphenicol showed an additive action up to 76%, nearly equal to the impact of the compounds separately. We conclude that the application of the bacterial test model of nonpathogenic B. subtilis VKPM B-4419 is likely to be promising for the design and prescreening of medicine, including tests for synergism and additivity of the combined action of phytochemical compounds and antibiotics.