As antibiotic resistance becomes a serious global health threat, food-grade bacteriocins—an antimicrobial peptide (AMP)—offer a promising new therapy, but their application is limited due to poor stability and low water solubility. To address this, we designed a carrier-free self-assembly strategy: a novel bacteriocin produced by lactic acid bacteria in fermented foods was modified to enhance its hydrophobicity, resulting in the spontaneous formation of nano antimicrobial bacteriocins (NAMBs) in TSB, LB, and MH media. These NAMBs exhibit broader antibacterial activity, with enhanced efficacy against both Gram-positive and Gram-negative pathogens—including Listeria monocytogenes, Acinetobacter baumannii, and Vibrio parahaemolyticus—demonstrated by significantly lower in vitro inhibitory concentrations and improved in vivo therapeutic effects in infected mice. Mechanistic studies revealed targeted interference with cell envelope metabolism: in Listeria monocytogenes, NAMBs reinforce the peptidoglycan layer while reducing wall-associated diacids and lipoteichoic acids, impairing carbohydrate metabolism and membrane transport; in Acinetobacter baumannii, they decrease fatty acid synthesis, disrupt phospholipid composition, weaken lipopolysaccharide integrity, ultimately causing membrane instability and cell death. These dual actions—disrupting metabolic processes and remodeling bacterial cell walls or membranes—highlight the multifunctionality of NAMBs. Our carrier-free self-assembly approach overcomes the stability and solubility limitations of AMPs, paving the way for next-generation antibacterial therapies.