Genomic epidemiology and the evolution of erm(B)-mediated macrolide resistance in Campylobacter.

Campylobacter is a major foodborne bacterial pathogen that has become increasingly resistant to clinically important antimicrobials. Of particular concern is the emergence of erm(B)-mediated macrolide resistance, which has been increasingly documented across Campylobacter isolates from diverse ecological reservoirs. In this study, we investigated the genomic characteristics and epidemiology of erm(B)-carrying clinical Campylobacter isolates from Shanghai, alongside a globally representative dataset of all publicly available strains. Among clinical isolates obtained from a diarrhoeal outpatient surveillance programme between 2020 and 2023 in Shanghai, China, 16% (80/500) were erythromycin-resistant, with 23.8% (19/80) testing positive for erm(B). The genomes of these isolates were sequenced to identify erm(B) gene alleles. Phylogenetic analyses, pairwise comparisons of core and accessory genomes and examination of shared alleles revealed horizontal gene transfer as the predominant mechanism driving the transmission of erm(B) between isolates from various sources. Poultry was identified as a key reservoir for human infections caused by erm(B)-positive Campylobacter isolates. Comparative pangenome analyses of erm(B)-positive and negative isolates identified multiple accessory elements associated with erm(B) acquisition, among which the IS607 family transposon-associated tnpB gene exhibited sequence and structural homology to functional progenitors of CRISPR-Cas nucleases. These findings expand our understanding of the epidemiology of erm(B)-mediated macrolide resistance in Campylobacter and underscore the urgent need for enhanced antimicrobial stewardship in poultry production and targeted surveillance programmes to curb the spread of resistance.