The study investigates the role of *Klebsiella oxytoca* in providing colonization resistance (CR) against *Salmonella Typhimurium* through multiple mechanisms. *K. oxytoca* species complex, part of the human microbiome, can produce enterotoxins like tilimycin and tilivalline while also contributing to CR. The research combines ex vivo assays, CRISPR-mutagenesis, and mouse models to demonstrate that *K. oxytoca* provides CR against *S. Typhimurium*. In vitro, antimicrobial activity depends on tilimycin production and is induced by simple carbohydrates. In vivo, CR depends on toxin production in germ-free mice but is toxin-independent in mice with residual microbiota. Dulcitol utilization is essential for toxin-independent CR in gnotobiotic mice. These findings highlight that nutrient availability is key to both toxin-dependent and substrate-driven competition between *K. oxytoca* and *S. Typhimurium*.The study investigates the role of *Klebsiella oxytoca* in providing colonization resistance (CR) against *Salmonella Typhimurium* through multiple mechanisms. *K. oxytoca* species complex, part of the human microbiome, can produce enterotoxins like tilimycin and tilivalline while also contributing to CR. The research combines ex vivo assays, CRISPR-mutagenesis, and mouse models to demonstrate that *K. oxytoca* provides CR against *S. Typhimurium*. In vitro, antimicrobial activity depends on tilimycin production and is induced by simple carbohydrates. In vivo, CR depends on toxin production in germ-free mice but is toxin-independent in mice with residual microbiota. Dulcitol utilization is essential for toxin-independent CR in gnotobiotic mice. These findings highlight that nutrient availability is key to both toxin-dependent and substrate-driven competition between *K. oxytoca* and *S. Typhimurium*.