Evidence of transfer of antimicrobial resistance genes from the porcine pathogen Streptococcus suis to human clinical isolates of Streptococcus agalactiae in a major pig-producing region of Spain

This study demonstrates that the pig pathogen Streptococcus suis acts as a significant reservoir and transfer hub for antimicrobial resistance (AMR) genes that can spread to human-associated streptococci. In Spanish porcine isolates, resistance to erythromycin and tetracycline was driven by erm(B) and tet(O) genes located on mobile genetic elements (Tn5252-family ICEs/IMEs), which showed high variability and capacity to carry multiple resistance genes. Importantly, similar elements were identified in human clinical isolates—particularly S. agalactiae—with strong genetic overlap (>95%) to those found in pigs. Laboratory experiments confirmed that these elements can transfer between species (including S. pneumoniae and S. pyogenes) and recombine to generate new resistance profiles. The findings provide compelling evidence for direct interspecies AMR transmission linked to livestock production, highlighting the critical need for integrated One Health surveillance and interventions targeting mobile genetic elements.