The widespread use of antimicrobials in poultry production has led to the emergence of multidrug-resistant (MDR) Campylobacter jejuni (C. jejuni), which can be directly transmitted from poultry to humans. This study aimed to investigate the antimicrobial resistance patterns and genetic relatedness of MDR C. jejuni isolates obtained from human and poultry using whole-genome sequencing (WGS). A total of 154 C. jejuni isolates were obtained, including 100 isolates from human samples and 54 from poultry samples. Antimicrobial susceptibility testing was performed using minimum inhibitory concentrations. We conducted WGS for MDR C. jejuni isolates using Oxford Nanopore platforms, followed by multiple bioinformatics analyses. Multilocus sequence typing profiles were used to characterize the genomes. Among all 154 C. jejuni isolates, high resistance rates were observed for ciprofloxacin (93.5%; 144/154), nalidixic acid (93.5%; 144/154), and tetracycline (40.9%; 63/154). Based on the MDR definition, 47 isolates were classified as MDR and selected for further genomic analysis. The most frequently observed MDR profile was resistance to fluoroquinolones, quinolones, and tetracyclines with human isolates exhibiting greater variability in their resistance patterns. The clonal complexes (CC) identified as overlapping in both poultry and human isolates included CC-21 and CC-45. Nine pTet-like plasmids were identified, all of which contained analogous sets of genes and a complete type IV secretion system. Whole-genome analysis of MDR C. jejuni strains isolated from humans and poultry revealed both genetic diversity and conserved genomic features, highlighting their evolutionary relatedness and potential for zoonotic transmission. Detection of plasmids carrying both antimicrobial resistance and virulence genes underscores the need for heightened surveillance to prevent zoonotic transmission.

To Cite This Article: Ahn HJ, Do KH, Ryu DH, Choe SJ, Kim MG, Go YK, Kim SB, Park YK, Kim SY and Seo KW, 2026. Genetic relatedness and molecular characterization of multidrug-resistant Campylobacter jejuni isolated from humans and poultry in Korea. Pak Vet J, 46(8): 2055-2066. http://dx.doi.org/10.29261/pakvetj/2026.186