Anti-Restriction Protein, KlcAHS, 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, KlcAHS, represents a novel mechanism that facilitates the increased transfer of bla(KPC-2) and KlcA(HS)-carrying plasmids among K. pneumoniae strains.