Genomic characterization of <i>Klebsiella</i> spp. from bovine mastitis: dissemination of a conserved, highly transmissible <i>lac</i> _acq ⁺ <i>fec</i> ⁺ plasmid drives burden of disease

Understanding the genetic basis of <i>Klebsiella</i>-induced mastitis is essential for improving prevention and control strategies. Our study reveals that the key mastitis-associated traits-lactose utilization (<i>lac</i>_acq) and iron acquisition (<i>fec</i>)-are commonly encoded on plasmids. The discovery of an identical conjugative plasmid in diverse <i>Klebsiella pneumoniae</i> lineages highlights the potential for rapid and widespread dissemination of virulence traits, independent of clonal background. However, we also show that clonal spread-combined with the vertical inheritance of a <i>lac</i>_acq⁺ <i>fec</i>⁺ plasmid-contributes to the success of <i>K. pneumoniae</i> ST107, a globally prevalent mastitis lineage. Together, our findings highlight the central role of mobile genetic elements in the ecology of mastitis-associated <i>Klebsiella</i>.