Provided herein are methods for increasing the therapeutic efficiency of oncolytic bacterial therapeutics. Bacterial oncolytic therapies, especially the ones targeting tumor hypoxia such as C. novyi-NT, often encounter incomplete tumor clearance in less hypoxic tumoral areas and severe inflammatory reactions. In this study, we explored immune-modulating preconditioning to suppress the host neutrophils and significantly enhanced the antitumor efficacy of C. novyi-NT in animal models, including an orthotopic brain tumor model in rabbits. The optimized preconditioning agent, hydroxyurea, is clinically approved and C. novyi-NT has demonstrated manageable safety and promising antitumor responses in clinical trials. Thus, the proposed preconditioning of neutrophil suppression is readily translatable to patients undergoing C. novyi-NT trials or other oncolytic biologic therapies and could improve outcome.