Campylobacter hepaticus Transcriptomics Revealed the Genes Involved in the Spotty Liver Disease (SLD) Pathogenesis

Campylobacter hepaticus is the etiologic agent of Spotty Liver Disease (SLD), a newly emerging bacterial disease of laying hens resulting in massive mortality and production losses primarily in free-range systems. Although its economic impact continues to grow, the molecular basis of C. hepaticus pathogenesis is poorly understood. In this study, we conducted transcriptomic profiling of C. hepaticus in three host-relevant conditions, exposure to chicken bile, infection of a chicken liver hepatocellular carcinoma (LMH) cell line, and isolation from liver lesions of naturally infected chickens. Through RNA-seq analysis, we found unique gene expression signatures in each environment. In bile, C. hepaticus exhibited differential expression of 412 genes, with upregulation of genes related to motility, cell envelope remodeling, glycosylation, nitrate respiration, and multidrug efflux systems, indicating a stress-adaptive, metabolically active lifestyle. In LMH cells, on the other hand, 125 genes were differentially expressed, primarily reflecting downregulation of motility, oxidative stress response, chaperones, and core metabolic processes, which suggests of a low-activity, intracellular dormant lifestyle. Transcriptomic analysis of C. hepaticus isolated from the liver identified 26 differentially expressed genes, featuring selective upregulation of nitrate respiration, sulfur metabolism, and pyridoxal 5’ phosphate (PLP) homeostasis, along with down regulation the major outer membrane porin (mompA), stress response chaperones (dnaK, groL), and genes involved in oxidative stress defense and energy production-. Further, immune evasion-related gene cmeA and a glycosyltransferase were found to be highly upregulated. This work presents the first in-depth transcriptomic exploration of C. hepaticus in multiple host relevant niches. Our findings reveal niche-specific gene expression profiles and highlight metabolic and structural accommodations allowing C. hepaticus survival during bile exposure, persistence within host cells, and induction of liver pathology. These insights provide a basis for the identification of novel virulence determinants and may inform the development of targeted interventions, including vaccines or antimicrobial therapy, to control SLD in commercial poultry operations.