Effects of EGCg and theaflavins on emetic toxin-producing Bacillus cereus in vitro

Bacillus cereus is a spore-forming foodborne pathogen that causes emetic and diarrheal food poisoning. An emetic strain of B. cereus produces spores and an emetic toxin called cereulide, which exhibits high heat resistance. In this study, we investigated the effects of epigallocatechin gallate (EGCg), theaflavin-3’-gallate (TF2b), and theaflavin-3,3’-gallate (TF3), polyphenolic components of tea extracts, on the survivability, spores, and toxin of B. cereus. Among them, EGCg at 62.5 μg/mL and 250 μg/mL showed bacteriostatic and bactericidal effects on B. cereus by damaging the cellular membrane, causing leakage of cellular nucleic acid related substances, and thus inhibiting the growth of B. cereus. However, no significant effects were shown on spore germination by EGCg, TF2b, or TF3 at a concentration of 250 μg/mL in this investigation. Their inhibitory effects were primarily confined to the outgrowth of daughter cells after spore germination. Furthermore, quantitative polymerase chain reaction (qPCR) showed that they suppressed the activity of cesA, a gene associated with cereulide production. At concentrations of 125 µg/mL for TF2b and 62.5 µg/mL for TF3, a discernible attenuation of cytotoxic effects induced by cereulide on HEp-2 cells was evident.