Antimicrobial Resistance and Molecular Epidemiology of Campylobacter Isolates from Foodborne Illness Cases in Saitama, Japan.

Campylobacter jejuni and C. coli are major causes of foodborne illness worldwide. Increasing antimicrobial resistance (AMR) and the implication of C. jejuni in Guillain-Barré syndrome (GBS), a post-infectious complication, are serious public health concerns. In this study, we characterized Campylobacter isolates from foodborne illness cases in Saitama Prefecture, Japan, focusing on AMR profiles, CPS (Penner) genotypes, multilocus sequence types (STs), and GBS-associated LOS biosynthesis genes. High resistance rates to quinolones and tetracycline were observed in C. jejuni (46.6%, 26.4%) and C. coli (50.0%, 60.0%), and C. coli also showed erythromycin resistance (25.0%), whereas C. jejuni remained susceptible. CPS genotyping of 148 C. jejuni isolates showed a high typeability rate (97.3%), supporting its utility for molecular surveillance. In a 40-isolate C. jejuni subset, MLST revealed that clonal complex 21 (CC21) predominated and ST-4526 was the most common ST. All ST-4526 isolates were quinolone-resistant and carried the GBS-associated genes cst-II (Thr51 variant), cgtA, and cgtB. The ST distribution of C. jejuni overlapped with that of chicken-derived strains, suggesting poultry as a major source of infection. These findings highlight the utility of CPS genotyping and the public health importance of the quinolone-resistant ST-4526 lineage carrying GBS-associated LOS biosynthesis genes.