Genomic insights and survival dynamics of Campylobacter from ruminants in UHT milk, raw milk and dairy products

Broiler meat is the primary foodborne source of Campylobacter iosis; however, the discrepancy between reported human cases and recorded outbreaks worldwide suggests the need to investigate additional exposure sources. Milk is particularly relevant due to its association with outbreaks linked to raw milk consumption or inadequate pasteurization. Considering the role of ruminants as Campylobacter reservoirs, this study was undertaken to investigate Campylobacter prevalence on carcasses and intestinal contents of cattle and sheep sampled at slaughterhouses, as well as in raw milk and dairy products from farms and dairies. Whole-genome sequencing (WGS) was used to analyze the population structure, virulence, and antimicrobial resistance of 385 C. jejuni and C. coli isolates from cattle and sheep in Italy. Additionally, the survival of three C. jejuni strains was assessed in raw milk, UHT milk, and ricotta cheese under different temperatures and time points, using standard culture-based enumeration methods. Genome analysis revealed genetic diversity among ruminant isolates, with a pronounced host-specific structuring of Campylobacter populations. While CC206 and CC21 were the predominant clonal complexes overall, several lineages showed strict host association. CC658 was exclusively detected in sheep, whereas CC353, CC45, and CC49 were confined to cattle, indicating strong host-adapted patterns. Only two sequence types (ST1055 and ST10304) were shared between cattle and sheep, highlighting limited cross-host overlap and suggesting restricted interspecies transmission. 14 strains of animal and food origin exhibited a higher number of virulence-associated genes, while fewer than 10% showed multi-resistance to at least three antibiotic classes. Moreover, C. jejuni strains exhibited considerable resistance to refrigeration and dairy processing conditions, with distinct survival patterns depending on the dairy matrix. In particular, the C. jejuni 8264ST-403 complex exhibited enhanced persistence in ricotta cheese compared with UHT and raw milk, remaining viable throughout the entire experimental period and maintaining an average concentration of 4.21 log10 CFU/g at 42 days post-inoculation. This survival in ricotta underscores the ability of specific C. jejuni lineages to withstand adverse conditions in fresh dairy products, highlighting a potential public health risk. With an increasing consumer preference for raw dairy products, enhanced surveillance and control measures are essential to mitigate associated risks.