Elucidation of the mechanisms involved in bacterial genome instability and, consequently, in the generation of new bacterial variants is still one of the principal goals that have not been completely achieved thus far. Understanding horizontal transfer of GIs is essential to elucidate how genome plasticity in S. suis is maintained and how it may contribute to the evolution of infectious diseases. Our work, which demonstrated the horizontal transfer of an important streptococcal PAI, provides an interesting insight into the molecular mechanism of GI transfer and may prove to be exemplary for the study of the evolutionary strategies of other pathogens. A better understanding of the molecular biology of PAIs will both greatly improve our knowledge of bacterial pathogenesis and may lead to new and improved vaccines, novel therapeutics and better environmental monitoring of epidemic strains.