Recombination between Streptococcus suis ICESsu32457 and Streptococcus agalactiae ICESa2603 yields a hybrid ICE transferable to Streptococcus pyogenes.

Abstract Integrative conjugative elements (ICEs) are mobile genetic elements that reside in the chromosome but retain the ability to undergo excision and to transfer by conjugation. Genes involved in drug resistance, virulence, or niche adaptation are often found among backbone genes as cargo DNA. We recently characterized in Streptococcus suis an ICE (ICE Ssu 32457) carrying resistance genes [ tet (O/W/32/O), tet (40), erm (B), aphA , and aadE ] in the 15K unstable genetic element, which is flanked by two ∼1.3 kb direct repeats. Remarkably, ∼1.3-kb sequences are conserved in ICE Sa 2603 of Streptococcus agalactiae 2603V/R, which carry heavy metal resistance genes cadC / cadA and mer . In matings between S. suis 32457 (donor) and S. agalactiae 2603V/R (recipient), transconjugants were obtained. PCR experiments, PFGE, and sequence analysis of transconjugants demonstrated a tandem array between ICE Ssu 32457 and ICE Sa 2603. Matings between tandem array-containing S. agalactiae 2603V/R (donor) and Streptococcus pyogenes RF12 (recipient) yielded a single transconjugant containing a hybrid ICE, here named ICE Sa 2603/ICE Ssu 32457. The hybrid formed by recombination of the left ∼1.3-kb sequence of ICE Ssu 32457 and the ∼1.3-kb sequence of ICE Sa 2603. Interestingly, the hybrid ICE was transferable between S. pyogenes strains, thus demonstrating that it behaves as a conventional ICE. These findings suggest that both tandem arrays and hybrid ICEs may contribute to the evolution of antibiotic resistance in streptococci, creating novel mobile elements capable of disseminating new combinations of antibiotic resistance genes.