Anti‑restriction protein KlcAHS enhances carbapenem resistance

The KlcAHS gene was previously identified as coexisting with the blaKPC‑2 gene in the backbone region of a series of blaKPC‑2‑harboring plasmids. The purpose of the present study was to determine the association between the KlcAHS and blaKPC‑2 genes. KlcAHS deletion and complementation experiments were used to evaluate the association between KlcAHS and carbapenem minimal inhibition concentrations (MICs). Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis was used to detect changes in the expression levels of blaKPC‑2 upon knocking out the KlcAHS gene in a blaKPC‑2‑harboring plasmid. The imipenem MIC of the transformants harboring ΔKlcAHSpHS10842 was lower (16 µg/ml) than that of the transformants harboring wild‑type pHS10842 (32 µg/ml), whereas the kanamycin MIC of the transformants harboring pET24a was lower (1,024 µg/ml) than that of the transformants harboring pET24a‑KlcAHS (2,048 µg/ml). The imipenem MICs of the two NM1049 Escherichia coli strains carrying plasmids pHS092839 or ΔKlcAHSpHS092839 exceeded 16 µg/ml, whereas the ertapenem MIC of the host strains harboring ΔKlcAHSpHS092839 was 4 µg/ml compared with ≥8 µg/ml observed in the host strains carrying pHS092839. The RT‑qPCR results demonstrated that the messenger RNA expression levels of blaKPC‑2 in the transformants carrying ΔKlcAHSpHS092839 were significantly downregulated (P=0.007) compared with those in the transformants carrying pHS092839. These findings revealed that KlcAHS elevated the MIC values of various antibiotics by upregulating the expression levels of blaKPC‑2. Therefore, KlcAHS can confer increased resistance to carbapenems in host strains. The survival probability of clinical pathogens may be enhanced by the presence of the KlcAHS gene in antibiotics used on a large scale.

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, KlcA_HS, represents a novel mechanism that facilitates the increased transfer of bla_KPC-2 and KlcA_HS-carrying plasmids among K. pneumoniae strains.