Emergence of cfr(C) variant in Campylobacter coli derived food-producing animal origin

Campylobacter is the leading cause of foodborne bacterial gastroenteritis globally. The cfr(C) gene encodes a 23S rRNA methyltransferase conferring cross-resistance to multiple classes of antibiotics. Here, we identified three novel cfr(C) variants in C. coli of swine origin. Compared to the original cfr(C), cfr(C)-variant-69 carried substitutions (Glu94Ala, Pro159Leu, Lys178Gln, Ile318Val), and cfr(C)-variant-104 and cfr(C)-variant-1921C17 harbored frame-shift mutations. Functional assay demonstrated that only cfr(C)-variant-69 conferred elevated MIC values 8-fold (florfenicol), 4-fold (chloramphenicol), and 2-fold (linezolid) compared to the parental strain NCTC 11168, respectively. In addition, a total of 67 C. coli isolates were identified to carry cfr(C) (64 from Genbank database and three from this study). WGS analysis revealed the global distribution of cfr(C) across five countries. MLST analysis indicated that 22 distinct sequence types were associated with cfr(C) dissemination, with ST1068 representing the predominant lineage. wg-MLST analysis stratified by collection time, geographic origin, and source, revealed significant clonal relatedness among strains from different years, countries, or origins. Furthermore, 18 distinct genetic environments flanking cfr(C) were identified among the isolates, with type 11 representing the predominant genotype [hph-pcp-hp-aphA3-cfr(C)-hp-hp]. Notably, the cfr(C) gene was flanked by multiple transposable elements (ISAcsp6, ISCco2, ISChh1, ISEncal, and ISSag10) across different genetic contexts, in which ISAcsp6 and ISEncal were firstly reported. In conclusion, we identified a novel functional cfr(C) variant in poultry-derived C. coli and characterized the global dissemination of cfr(C), demonstrating both horizontal gene transfer and regional clonal expansion among C. coli. One Health genomic surveillance for cfr(C)-positive Campylobacter spp. is critical to mitigate this escalating antimicrobial resistance threat.