Comprehensive genomic insights into lineages, virulence, and antibiotic resistance profiles of Campylobacter jejuni entailing a global One Health scenario

Campylobacter species are among the leading causes of bacterial gastroenteritis worldwide, with poultry recognized as a major reservoir for several life-threatening foodborne and zoonotic infections. The overuse and possible misuse of antimicrobials in the livestock sector in different countries of the world have contributed to the emergence of multidrug-resistant Campylobacter jejuni strains with significant public health concerns. To better understand the evolution, host adaptation, and antimicrobial resistance (AMR) of C. jejuni , we performed a global comparative genomic analysis of 1,125 high-quality genomes from human and chicken hosts, including five newly sequenced isolates representing broiler chicken samples. Pangenome analysis of 1,125 C. jejuni genomes identified 4,489 orthologous gene clusters, of which 1,360 constitute the conserved core genome. The findings indicate a weakly open pangenome approaching saturation, suggesting limited gene acquisition. Phylogenomic analysis revealed three major clades with limited geographic clustering, consistent with global dissemination and evolutionary divergence. Human isolates were distributed across all clades, whereas chicken isolates were primarily restricted to clade one. Sequence typing identified 290 STs across 30 clonal complexes, with ST-48 enriched in chickens while ST-50 predominated in humans, reflecting potential host adaptation and epidemiological structuring. All five in-house isolates were multidrug-resistant, producing extended-spectrum β-lactamases (ESBLs) that conferred β-lactam resistance. Additionally, three isolates exhibited resistance to macrolides and tetracycline, further underscoring their broad resistance phenotype. Genome-wide AMR profiling of 1,125 C. jejuni isolates identified 31 well-characterized resistance genes, including those encoding RND and MATE efflux systems, penicillin-binding proteins, and metallo- and serine-beta-lactamase families, underscoring their intrinsic role in the core resistome. The most common resistance mutations were gyr A p.T86I (60.3%) and 23S r2075A>G (4%), conferring resistance to fluoroquinolones and clarithromycin. Analysis of the 1,125 genomes, including the five new isolates, revealed 126 key virulence genes, with cytolethal distending toxin ( cdt A, cdt B, and cdt C) and capsule biosynthesis clusters present in over 85% and 93% of the isolates, respectively. These findings provide comprehensive insights into the evolution, transmission dynamics, host adaptation, antimicrobial resistance, and pathogenic potential of C. jejuni . Poultry serves as a critical reservoir contributing to the emergence and dissemination of high-risk, pathogenic, and drug-resistant lineages, underscoring the importance of monitoring and controlling AMR in livestock to protect public health.