Effects of camellia saponins on biofilm formation and virulence factor genes of Bacillus cereus

Bacillus cereus is a common foodborne pathogen that can cause vomiting or diarrheal food poisoning and may not be suppressed using conventional cleaning procedures due to its ability to form biofilms. Biofilms have brought enormous challenges to the food safety industry. Camellia saponins are a class of oleanolanetype pentacyclic triterpenoid saponins that naturally exist in Camellia oleifera. This study demonstrated that the MBIC of camellia saponins against B. cereus was 64 mg/mL, and that the inhibitory effects on B. cereus upon adding saponins at different time periods varied as shown via scanning electron microscopy. However, the best inhibitory effect on biofilms was achieved through the addition of 1 mL of camellia saponins (1/2 MBIC) initially and adding 1 mL of camellia saponins (1/2 MBIC) again after 12 h, resulting in a decreased secretion of extracellular polymers and weakening the ability of the bacteria to form biofilms. The results showed that the swarming motility was significantly inhibited by camellia saponins. Furthermore, in the process of biofilm formation, camellia saponins could inhibit the production of extracellular proteins. qRT-PCR showed that the expression of six enterotoxin B. cereus virulence genes (hblA, hblD, cerA, cerB, nheA and hlyIII) was significantly inhibited by camellia saponins.