Lactobacillus rhamnosus GR-1 attenuates foodborne Bacillus cereus-induced the NLRP3 inflammasome activity in bovine mammary epithelial cells by protecting intercellular tight junctions

Abstract Background: Bacillus cereus (B. cereus) is one of the important pathogens of human food poisoning that causes diarrhea and vomiting. B. cereus can induce mastitis with strong survival ability, which cannot be inactivated by high-temperature short-time pasteurization conditions. Therefore, B. cereus has the opportunity to enter the market through pasteurized milk and dairy products, causing great hidden dangers to food safety and human health. Results: In this study, B. cereus 2101 (BC) was isolated from dairy cow milk samples with mastitis. BC secreted HBL, NHE, InhA, Hemolysin A, Hemolysin III, CytK, EntFM, and tolerated to AMP, AMC, AZI, CZ, CIP, STR, and TE. BC grew rapidly with strong hemolysis, which caused great difficulties in the prevention of mastitis and food security. MAC-T cells were treated with BC and / or Lactobacillus rhamnosus GR-1 (LGR-1), and the results showed that pretreatment with LGR-1 protected the integrity of tight junction and the expression of ZO-1 and Occludin destroyed by BC. Besides, we also found out that pretreatment with LGR-1 reduced the expression of NLRP3, ASC, Caspase1 p20, GSDMD p30, inflammatory factors (IL-1β and IL-18) and cell death induced by BC. These indicators are related to the NLRP3 inflammasome activity. Moreover, pretreatment with LGR-1 reduced the NLRP3 inflammasome activity, and increased the expression of ZO-1 and Occludin induced by LPS + ATP stimulation. MAC-T cells were transfected with NLRP3 siRNA for 5 h or MCC950 (NLRP3 inhibitor) for 0.5 h and / or treated with BC and / or LGR-1 for 3 h. NLRP3-siRNA transfection and MCC950 attenuated the NLRP3 inflammasome activity induced by BC. The expression of inflammatory cytokines and cell death suggested that the inflammatory pathway might play an important role in the induction of NLRP3 inflammasome by BC and the protection of LGR-1. Conclusions: These results suggest that LGR-1 might be a probiotic for the alternative to antibiotics and could be administered to prevent mastitis in dairy cows to ensure food security.