Monomorphic genotypes within a generalist lineage of Campylobacter jejuni show signs of global dispersion

Abstract

The decreased costs of genome sequencing have increased capability to apply whole-genome sequence on epidemiological surveillance of zoonotic Campylobacter jejuni. However, knowledge about how genetically similar epidemiologically linked isolates can be is vital for correct application of this methodology. To address this issue in C. jejuni we investigated the spatial and temporal signals in the genomes of a major clonal complex and generalist lineage, ST-45 CC, by exploiting the population structure and genealogy and applying genome-wide association analysis of 340 isolates from across Europe collected over a wide time-range. The occurrence and strength of the geographical signal varied between sublineages and followed the clonal frame when present, while no evidence of a temporal signal was found. Certain sublineages of ST-45 CC formed discrete and genetically isolated clades to which geography and time had left only negligible traces in the genomes. We hypothesize that these ST-45 CC clades form globally expanded monomorphic clones possibly spread across Europe by migratory birds. In addition, we observed an incongruence between the genealogy of the strains and MLST typing, thereby challenging the existing clonal complex definition and use of a common MLST-based nomenclature for the ST-45 CC of C. jejuni.