Comparative Genomic Analysis of Livestock-Derived Campylobacter jejuni: Antimicrobial Resistance, Virulence, Mobile Genetic Elements, and Genetic Relatedness.

Campylobacter jejuni is a major cause of foodborne illnesses, and its increasing antimicrobial resistance (AMR) poses serious public health risks. Owing to their high genetic diversity and frequent intraspecific recombination, understanding the virulence traits of Campylobacter remains challenging. We elucidated the resistance and virulence mechanisms of C. jejuni in livestock using comparative genomic and phenotypic analyses. We analyzed C. jejuni strains isolated from chicken meat, chicken slaughterhouses, and dairy cattle farms. High resistance rates were observed for nalidixic acid, ciprofloxacin, and tetracycline. The chicken-derived strains showed significantly higher tetracycline resistance and marginally higher nalidixic acid resistance, whereas the cattle-derived strains showed marginally higher ciprofloxacin resistance. The key AMR determinants included gyrA and tet(O), which were correlated with resistance phenotypes. Ten virulence factor families were identified with prevalences exceeding 90%. Biofilm formation was observed in 31.9% of strains and correlated with flagella-associated virulence factors. Eighteen plasmid types were detected, primarily in the pTet family, which carried various AMR genes and components of the Type IV secretion system, potentially facilitating the co-transfer of resistance and virulence traits. Conjugation experiments confirmed the horizontal transfer of two pTet plasmid types into the wild-type C. jejuni strain. Further, our analyses revealed over 95% genetic similarity with European C. jejuni strains in a public database-supporting the hypothesis of zoonotic transmission via global food chains-and the zoonotic risks of livestock-derived Campylobacter jejuni. These findings emphasize the need for extended global surveillance to mitigate the risk of zoonotic transmission.