Brucellosis caused by Brucella melitensis is a worldwide zoonotic disease, yet the role of the c-di-GMP phosphodiesterase BpdB in virulence remains incompletely understood. This study aimed to investigate the function of BpdB in B. melitensis pathogenicity and its involvement in host STING signaling. A bpdB deletion strain (ΔbpdB) and a complemented strain (CbpdB) were constructed in B. melitensis M5. Bacterial growth, stress tolerance, intracellular survival in macrophages, cytokine expression, and mouse virulence were evaluated. Deletion of bpdB did not affect in vitro growth but significantly attenuated virulence in BALB/c mice, reducing splenomegaly, splenic bacterial load, and hepatic granuloma formation. The ΔbpdB strain exhibited enhanced sensitivity to oxidative stress, whereas resistance to acid, polymyxin B, and SDS remained unchanged. Intracellular survival of ΔbpdB in RAW264.7 macrophages was reduced at 72 h post infection, a defect that was completely abrogated in STING-knockout RAW264.7 cells. ΔbpdB infection induced higher transcriptional levels of IFN-β and IL-1β, with IFN-β induction strictly dependent on STING. In C57BL/6J mice, the virulence attenuation of ΔbpdB was partially STING-dependent, as the reduction in splenic bacterial load was smaller in STING-knockout than in wild-type mice. These findings demonstrate that BpdB contributes to B. melitensis virulence by enhancing oxidative stress resistance and dampening STING-dependent host responses, providing new insights into c-di-GMP-mediated host–pathogen interactions.
Na Li, Qiumei Shi, Simin Chen et al.· International Journal of Mol...· 0 citations
Avian pathogenic Escherichia coli (APEC) induces avian colibacillosis and brings huge economic losses to global poultry production. The small alarmone (p)ppGpp mediates the bacterial stringent response, a vital pathway modulating microbial stress adaptation and pathogenic capacity. The functions of the (p)ppGpp synthase gene relA in APEC pathogenesis remain poorly characterized. In this study, we constructed a relA deletion mutant (ΔrelA) and its complemented strain (CΔrelA). The phenotypic and pathogenic characteristics of these strains were investigated. The results showed that deletion of relA did not significantly affect bacterial growth or motility. However, the ΔrelA strain showed increased susceptibility to aminoglycoside antibiotics. Furthermore, the enhanced interbacterial competition of the mutant was associated with the upregulation of core genes in the type VI secretion system (T6SS). Importantly, relA was essential for APEC adhesion to and invasion of avian DF-1 cells, as well as for colonization and virulence in ducklings, where ΔrelA exhibited significantly attenuated infectivity and reduced bacterial loads in the liver and spleen. Furthermore, transcriptomic analysis revealed that RelA deletion downregulated genes involved in integral components of the membrane, and further assays confirmed compromised membrane integrity in the mutant strain. These findings suggest that RelA maintains membrane integrity, which underpins its contributions to antibiotic resistance and virulence. These findings indicate that relA plays a key role in APEC virulence, antibiotic resistance, and membrane homeostasis, and could provide a theoretical basis for targeting the stringent response as a potential strategy to control avian colibacillosis.
Jiangang Hu, Dossêh Jean Apôtre Afayibo, Chang Liu et al.· Microorganisms· 0 citations
Results demonstrate that PlsC is essential for maintaining membrane homeostasis and stress resistance in Brucella, which in turn supports its survival within professional phagocytes and full virulence in vivo and suggests a critical link between phospholipid metabolism and Brucella pathogenicity.
Fazhi Xu, Yao Feng, Mengsi Li et al.· Veterinary Research· 0 citations