Nisin against Bacillus cereus spores: activity, characterization, and beef application

Heat-resistant spore-forming bacteria are a primary cause of spoilage in ready-to-eat (RTE) foods, and effective control of spore contamination is critical for food preservation. Nisin, a GRAS antimicrobial peptide, exhibits potent activity against spore-forming bacteria, but its stage-specific effects during spore germination and outgrowth remain unclear. Heat-resistant Bacillus species were identified as the dominant spoilage bacteria in spoiled cooked beef, and B. cereus was selected to evaluate inhibitory effects of nisin via phenotypic and transcriptomic assays. The minimum inhibitory concentration (MIC) of nisin against B. cereus spores was 400 µg/mL. Nisin slightly promoted spore germination, but significantly inhibited subsequent outgrowth of germinated spores. Time‑kill assays showed that 1 MIC nisin reduced viable counts to 3.09 log CFU/mL at 6 h compared with 8.05 log CFU/mL in controls; 2 MIC treatment for 2 h achieved a 0.65‑log reduction for intact spores but a 1.49‑log reduction for germinated spores. Nisin disrupted membrane permeability and integrity, triggered intracellular oxidative stress, leading to genomic DNA damage and reduced ATP synthesis. Transcriptomic analysis revealed 3049 differentially expressed genes, with disturbed energy metabolism and amino acid biosynthesis pathways. In cooked beef, nisin effectively inhibited B. cereus outgrowth and delayed product spoilage during storage. This study provides practical data support for nisin application to control spore-forming bacteria and extend the shelf life of RTE meat products.