The Role of Restriction-Modification Systems in the Horizontal Transfer of Carbapenem Resistance Genes in Klebsiella pneumoniae

Our findings revealed a consistent distribution of RM systems among the 428 K. pneumoniae strains across China and other countries, with Type II RM systems being predominant (98.7%). These systems recognize the methylation and restriction site CCWGG (W = A or T). In other clinically common carbapenem-resistant bacteria, such as Acinetobacter baumannii and Pseudomonas aeruginosa, the proportion of Type II RM systems is only 2%. However, in K. pneumoniae and Escherichia coli strains, the carriage rate of M.EcoRII methyltransferase is 100%. From the perspective of bacterial RM defense and the horizontal transfer of mobile genetic elements (MGEs), the methylation and restriction enzyme recognition sites in K. pneumoniae are characteristic of Type II RM systems, sharing the same recognition sequence CCWGG. This may suggests that the corresponding methylated MGEs in K. pneumoniae not only spread horizontally within the species but can also engage in gene exchange with carbapenem-resistant Escherichia coli (CREC) in clinical settings.