Clonal diversity and shifting lineages of multidrug-resistant Campylobacter among healthy food handlers in Japan

Abstract Aims Campylobacter jejuni and Campylobacter coli are leading causes of foodborne illnesses, including human enteritis and diarrhoea, in many countries. The prevalence of antibiotic-resistant Campylobacter is increasing in both developing and developed countries, with fluoroquinolone-resistant Campylobacter recognised as a priority pathogen among antibiotic-resistant bacteria. Surveillance of Campylobacter antimicrobial resistance (AMR) is conducted worldwide because of its public health importance. In this study, we characterised the antimicrobial resistance patterns and genomic diversity of C. jejuni and C. coli strains isolated from food handlers in Japan. Methods and Results Surveillance was conducted on 106 Campylobacter isolates from food handlers between 2008 and 2023. Species identification by 16S rRNA sequencing, antimicrobial susceptibility testing, and whole-genome sequencing of selected isolates were performed to characterise phenotypic and genotypic features, compare AMR profiles, and assess phylogeny. Multilocus sequence typing (MLST) identified 36 sequence types (STs), including three novel STs and 10 clonal complexes (CCs). Among C. jejuni, CC21 (20.6%) was the most prevalent, followed by CC353 (2.8%). In C. coli, CC828 (4.7%) was the most prevalent. The AMR profiles and resistance determinants were as follows: quinolones (68.2%); mutations in the quinolone resistance-determining region (gyrA T86I); tetracyclines (40.2%); acquisition of tet(O) and macrolides (2.8%); and mutations in the 23S rRNA gene (A2075G). ST4526 (8.4%), reported only in Japan, was the most prevalent; however, it has not been detected since 2021, suggesting recent ST diversification. Conclusions This study characterised the AMR profiles and genetic backgrounds of non-clinical human-derived Campylobacter strains isolated from food handlers.