Anti-Restriction Protein, KlcA(HS), Promotes Dissemination of Carbapenem Resistance

Carbapenemase-producing Klebsiella pneumoniae (KPC) has emerged and spread throughout the world. A retrospective analysis was performed on carbapenem-resistant K. pneumoniae isolated at our teaching hospital during the period 2009–2010, when the initial outbreak occurred. To determine the mechanism(s) that underlies the increased infectivity exhibited by KPC, Multilocus Sequence Typing (MLST) was conducted. A series of plasmids was also extracted, sequenced and analyzed. Concurrently, the complete sequences of bla(KPC−2)-harboring plasmids deposited in GenBank were summarized and aligned. The bla(KPC−2) and KlcA(HS) genes in the carbapenem-resistant K. pneumoniae isolates were examined. E. coli strains, carrying different Type I Restriction and Modification (RM) systems, were selected to study the interaction between RM systems, anti-RM systems and horizontal gene transfer (HGT). The ST11 clone predominated among 102 carbapenem-resistant K. pneumoniae isolates, all harbored the bla(KPC−2) gene; 98% contained the KlcA(HS) gene. KlcA(HS) was one of the core genes in the backbone region of most bla(KPC−2) carrying plasmids. Type I RM systems in the host bacteria reduced the rate of pHS10842 plasmid transformation by 30- to 40-fold. Presence of the anti-restriction protein, KlcA(HS), on the other hand, increased transformation efficiency by 3- to 6-fold. These results indicate that RM systems can significantly restrict HGT. In contrast, KlcA(HS) can disrupt the RM systems and promote HGT by transformation. These findings suggest that the anti-restriction protein, KlcA(HS), represents a novel mechanism that facilitates the increased transfer of bla(KPC-2) and KlcA(HS)-carrying plasmids among K. pneumoniae strains.