The present invention is directed to mutant Salmonella sp. having a genetically modified msbB gene in which the mutant Salmonella is capable of targeting solid tumors. The invention is also directed to Salmonella sp. containing a genetically modified msbB gene as well as an genetic modification in a biosynthetic pathway gene such as the purl gene. The present invention further relates to the therapeutic use of the mutant Salmonella for growth inhibition and/or reduction in volume of solid tumors.