Genomic insights into Campylobacter jejuni from Norwegian broilers: high genetic diversity and limited persistence on farms

Campylobacteriosis is the most common foodborne illness in Norway, and consumption of fresh broiler meat is identified as a significant risk factor for human campylobacteriosis. Up to 2024, data from the Norwegian surveillance programme for Campylobacter suggest that a limited number of farms account for the majority of positive flocks. We therefore analysed Campylobacter spp. prevalence from 2009 to 2022 and sequenced biobanked isolates collected from flocks on farms with recurrent Campylobacter spp. positive flocks (case) and flocks from farms with a few and sporadically Campylobacter spp. positive flocks (control) in the period 2011–2022. The aim was to determine if the same C. jejuni strain persisted on case farms over time and to compare isolates across farms to investigate whether clonal spread of C. jejuni occurs in Norwegian broiler production. Further, we wanted to investigate whether isolates from case farms carry genes that favour infectiousness, colonisation and persistence in broilers or their environment, compared to isolates from control farms. We identified 69 control farms (75 isolates) and 15 case farms (42 isolates), resulting in cultivation of 117 isolates, all from unique flocks for WGS. Overall, 40 different MLST profiles were identified. Most isolates from case farms had different MLST profiles across years, suggesting introduction of new strains rather than persistent strains across years. ST-45 was the most frequently reported (n = 27, 23.1%) ST overall, reported in 9 of 42 (21.4%) isolates from case farms and 18 of 75 (24.0%) isolates from control farms. Further investigation of the isolates with cgMLST, suggested some, but not widespread, clonal dissemination, and that persistence of Campylobacter spp. strains on Norwegian farms is rare. The strains from case farms were significantly associated with the three genes pglD, flgG and legH. This current case control study indicates that C. jejuni strains do not persist in Campylobacter spp. positive Norwegian broiler farms across years.