The HvfB operon of Pasteurella multocida: An engineered deletion mutant provides cross-protection as an attenuated candidate vaccine strain

Pasteurella multocida (P. multocida) causes a broad spectrum of zoonotic diseases through various virulence factors, imposing substantial economic burdens on the global livestock industry. hvfB is a component of the hvf operon encoding multinuclear non-heme iron oxidases (MNIO). However, the precise mechanism by which hvfB regulates virulence of P. multocida remains largely unknown. In this study, an hvfB deletion strain was generated using homologous recombination. Using a combination of in vitro and in vivo assays, we characterized the mutant strain by analyzing its growth properties, pathogenic potential, transcriptional regulatory networks, and ability to interact with host immune and inflammatory pathways. The results showed that hvfB promotes bacterial growth, modulates capsule synthesis, enhances stress resistance in the PmCQ2 strain, and facilitates resistance to macrophage phagocytosis. Consequently, loss of hvfB markedly attenuated P. multocida pathogenicity, as evidenced by reduced bacterial loads in tissues and decreased levels of inflammatory factors. Transcriptomic analysis further revealed that hvfB influences stress resistance and virulence by affecting pathways associated with carbon metabolism, capsule synthesis, biofilm formation, and adhesion. Notably, the hvfB deletion strain conferred robust cross-protective immunity against P. multocida serotypes A and B. Collectively, these findings elucidate the pathogenic role of hvfB in P. multocida and support the potential of the hvfB deletion strain as an attenuated vaccine candidate against serotypes A and B.