, a common pathogen responsible for bloodstream infections, can evade clearance by the complement-dependent killing in serum, known as serum resistance. However, strategy in managing serum resistance is still lacking. In this study, we employed metabolomics to identify the metabolic features of . We found that the pyruvate/TCA cycle and alanine, aspartate, and glutamate metabolic pathways were significantly downregulated. Proline, identified as a key biomarker, effectively increased the serum sensitivity to multiple clinical isolates and restored the bactericidal activity of complement. The synergistic effect of proline was validated in a murine infection model. Furthermore, we demonstrated that proline activates the pyruvate/TCA cycle, increases proton motive force, and enhances complement proteins binding to bacterial surface, forming membrane attack complex to kill serum-resistant . Our findings provide new insights for the development of metabolism-based approach to manage serum resistance and offer potential targets and strategies for host immunity-based anti-infection therapies.