Synergistic antibacterial activities of nisin with tea polyphenol, and rhamnolipid against Bacillus cereus and the applications in pasteurized milk and cooked rice

Bacillus cereus, a well-known foodborne pathogen, frequently contaminates a wide range of food products, thereby posing a significant threat to food safety. The aim of this study was to investigate the combined antimicrobial effects of nisin (NS), tea polyphenol (TP) and rhamnolipid (RL) against B. cereus. The minimum inhibitory concentrations of NS, RL, and TP against B. cereus were determined to be 2 mg/mL, 2 mg/mL, and 0.25 mg/mL, respectively. The checkerboard tests demonstrated that the binary combinations of NS and RL (NS-RL), as well as NS and TP (NS-TP), exhibited synergistic effects, with fractional inhibitory concentration indices (FICIs) of 0.5. In contrast, the combination of TP and RL (TP-RL) showed an additive effect (FICI = 0.75). The results of the antibacterial mechanism studies indicated that NS-TP synergistically induced cell membrane damage and promoted the efflux of intracellular substances from B. cereus. Additionally, TP-RL also facilitated the leakage of intracellular components. Meanwhile, the analysis of intracellular reactive oxygen species (ROS) levels revealed that NS-RL synergistically enhanced the accumulation of intracellular ROS. Furthermore, in the context of pasteurized whole milk and cooked rice, the addition of 0.13 mg/mL of TP and 1 mg/mL of RL significantly enhanced the antimicrobial activity of 1 mg/mL NS. This study provides valuable scientific insights for the application of these natural antimicrobials in food preservation, which is conducive to enhancing food safety and extending the shelf-life of food products.