Anti-restriction protein ArdA promotes clinical Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae spread and its molecular mechanism

Background Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has spread worldwide and has become a major threat to public health. The restriction modification system provides an innate defence of bacteria against plasmids or transposons, while many different types of plasmid encoding the anti-restriction protein ArdA can specifically affect the restriction activity in bacteria. Objectives To detect the codistribution of ArdA and bla(KPC-2) plasmids in KPC-KP and explore the molecular mechanism of ArdA promoting KPC-KP spread. Methods We collected 65 clinical CRKP isolates from Ningbo, China, and 68 cases of plasmid complete sequences in GenBank to determine the prevalence of ArdA gene on the K. pneumoniae bla(KPC-2) plasmid. The anti-restriction function of ArdA in promoting horizontal gene transfer (HGT) was verified by transformation, conjugation and transduction methods, and the pull-down experiment was used to investigate the molecular mechanism of ArdA protein in vitro. Results We found that ArdA was widely distributed in KPC-KP in 100% of cases, which was detected in 0% of drug susceptible K. pneumoniae, and the plasmids containing the ArdA gene in 90% of the 30 cases randomly retrieved from the database. We also verified that ArdA has a good anti-restriction function (P < 0.05) through two aspects of HGT (transformation, transduction), and explored the non-occurrence interaction of ArdA and the hsdM subunit protein of EcoKI enzyme from the perspective of protein molecules. Conclusions These findings suggest that the coexistence advantage of ArdA with the bla(KPC-2) plasmids may provide KPC-producing K. pneumoniae with a very efficient evasion of the restriction of type I systems, which not only favours ArdA-containing mobile genetic elements in the same species HGT between bacteria also facilitates HGT between other bacterial species.

Automated summary

This study investigated the co-distribution of ArdA and bla(KPC-2) plasmids in KPC-KP and explored the molecular mechanism of ArdA promoting KPC-KP spread. The results showed that ArdA was widely distributed in KPC-KP and had a good anti-restriction function. The coexistence of ArdA with bla(KPC-2) plasmids enables KPC-KP to evade restriction and facilitates gene transfer between bacterial species.