Strain-specific persistence ofin the C3HeB/FeJ mouse model of pulmonary infection.

Abstract

, a member of thecomplex (Bcc), causes severe, treatment-resistant lung infections in individuals with cystic fibrosis and chronic granulomatous disease.We hypothesized that the C3HeB/FeJ mouse strain, characterized by impaired macrophage-mediated immunity, would be susceptible to persistent infection by clinical Bcc isolates.To evaluate C3HeB/FeJ susceptibility to various Bcc isolates and characterize the macrophage-intrinsic responses and antibiotic susceptibility within this model.C3HeB/FeJ and C57BL/6 mice were compared for susceptibility to pulmonary infection withAU0728 following intratracheal inoculation. Bacterial persistence and extrapulmonary dissemination were monitored for up to 42 days. Host immune responses were assessed through systemic leucocyte profiling and analysis of bone marrow-derived macrophage (BMDM) function, including intracellular bacterial control, cytokine production and time-resolved cell-death responses. Model breadth was evaluated using three additional clinical Bcc isolates. Finally, theefficacy of high-dose ceftazidime or meropenem was assessed against established pulmonary infection.C3HeB/FeJ mice sustained significantly higher pulmonary burdens ofAU0728 than C57BL/6 mice, resulting in a stable, non-sterilizing infection with extrapulmonary dissemination lasting at least 42 days., C3HeB/FeJ BMDMs supported higher intracellular bacterial loads and failed to mount effective IFN-γ-dependent intracellular control. Mixed-effects modelling of cell-death responses revealed that both strains initiated early apoptotic signalling following infection; however, this response was attenuated in C3HeB/FeJ macrophages and was not restored by IFN-γ pretreatment. In contrast, late-stage membrane permeabilization increased progressively over time and exhibited strain- and IFN-γ-dependent modulation at later stages of infection. Susceptibility was highly strain-specific: three additional clinical Bcc isolates were rapidly cleared from C3HeB/FeJ lungs. Treatment with ceftazidime or meropenem reduced established pulmonary bacterial burdens by ~1.4-1.5 log₁₀ c.f.u. but did not achieve sterilization.These findings identify C3HeB/FeJ mice as a selectively susceptible host for sustained pulmonary infection byAU0728 and demonstrate that persistence in this model is strongly strain-dependent. Impaired macrophage-intrinsic IFN-γ-dependent control and stage-specific dysregulation of cell-death responses contribute to bacterial persistence. This immunocompetent mouse model provides a tractable platform for dissecting strain-level virulence mechanisms and for evaluating therapeutic strategies targeting chronic Bcc infection.