The mechanisms and effect of epigallocatechin gallate (EGCg) on the germination and proliferation of bacterial spores

Abstract

Spore-forming bacteria form highly stress-resistant spores in environmental conditions that are deleterious to growth, such as nutrient limitation, and are thus of particular concern in the food and beverage industry. Control of these bacteria is extremely important for food and beverage preservation. Catechins exhibit antibacterial action against the vegetative cells of a range of bacterial species, but the detailed mechanism of action of catechins on spores has not been clarified. In this study, the mechanism of antibacterial action of epigallocatechin gallate (EGCg) against spore-forming bacteria was examined. The effects of catechins on the germination of spores and vegetative cell growth of the genus Bacillus were investigated by chronological measurements of viable counts and spore counts cultured in medium containing EGCg, using total cell count and heat resistance cell count as indices of spores. The spore count was independent of the presence of EGCg and decreased immediately after the start of culture, whereas vegetative growth was suppressed by EGCg. It is therefore likely that EGCg does not inhibit spores, but acts on vegetative cells. We also analyzed the amount of EGCg adsorbed by vegetative cells and spores with an electron microscopic observation technique using cerium. The amount of EGCg adsorbed by spores was extremely small in comparison to that adsorbed by vegetative cells. Our findings indicate that the reason why catechins do not suppress spore germination or inactivate spores is that catechins are not adsorbed by spores and thus cannot act on them.