Fecal pathogenic bacteria transmit rank I high-risk ARGs through longitudinal and horizontal routes in swine

Antibiotic resistance genes (ARGs) in bacteria threaten both livestock and human health, with their transmission dynamics influenced by mobile genetic elements (MGEs) and host age. However, longitudinal studies tracking high-risk ARGs across the entire swine lifetime remain limited. Here, we analyzed 162 fecal samples from parental and offspring pigs throughout their growth stages using metagenomic sequencing to investigate potential vertical and horizontal ARG transmission pathways. The results showed that 260 subtypes belonging to 21 types of ARGs were identified, with tetracycline, aminoglycoside, macrolide-lincosamide-streptogramin (MLS), and multidrug resistance being predominant. A total of 130 subtypes of ARGs were shared between parents and offspring, among which 30 subtypes of Rank Ⅰ (the highest-risk) ARGs contributed significantly, mainly conferring resistance to aminoglycoside, MLS, tetracycline and multidrug antibiotics, suggesting potential vertical transmission from parental generation to the offspring. Co-occurrence network analysis indicated that pathogenic bacteria, particularly Escherichia coli , Salmonella enterica , and Shigella flexneri , may serve as potential hosts for Rank I ARGs, potentially facilitating their dissemination. Additionally, it was also found that these Rank I ARGs might be horizontally transmitted through the three core MGEs ( tnp A, IS 91, and Tn 916-orf13) by pathogenic bacteria. This study revealed the changes in resistome at different growth stages and the potential pathways for the vertical and horizontal transmission route of high-risk ARGs by pathogenic bacteria in swine, offering insights for developing control strategies. • A total of 130 ARG subtypes were vertically transmitted (parent-offspring) in swine • A total of 30 subtypes of Rank I ARGs persisted throughout the growth stage • Pathogenic bacteria vertically transmitted (parent-offspring) 30 Rank Ⅰ ARGs • Pathogenic bacteria spread Rank Ⅰ ARGs horizontally through the three core MGEs