Anti-Restriction Protein, KlcAHS, Promotes Dissemination of Carbapenem Resistance

Abstract

Carbapenemase-producing <i>Klebsiella pneumoniae</i> (KPC) has emerged and spread throughout the world. A retrospective analysis was performed on carbapenem-resistant <i>K. pneumoniae</i> 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 <i>bla</i>_KPC-2-harboring plasmids deposited in GenBank were summarized and aligned. The <i>bla</i>_KPC-2 and <i>KlcA</i>_<i>HS</i> genes in the carbapenem-resistant <i>K. pneumoniae</i> isolates were examined. <i>E. coli</i> 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 <i>K. pneumoniae</i> isolates, all harbored the <i>bla</i>_KPC-2 gene; 98% contained the <i>KlcA</i>_<i>HS</i> gene. <i>KlcA</i>_<i>HS</i> was one of the core genes in the backbone region of most <i>bla</i>_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 <i>bla</i>_KPC-2 and <i>KlcA</i>_<i>HS</i> -carrying plasmids among <i>K. pneumoniae</i> strains.