RES-Xre toxin-antitoxin locus maintains the stability of the virulence plasmid in .

Hypervirulent isolates have been increasingly reported worldwide especially hypervirulent drug-resistant variants owing to the acquisition of a mobilizable virulence plasmid by a carbapenem-resistant strain. This pLVPK-like mobilizable plasmid encodes various virulence factors; however, information about its genetic stability is lacking. This study aimed to investigate the type II toxin-antitoxin (TA) modules that facilitate the virulence plasmid to remain stable in . More than 3,000 TA loci in 2,000  plasmids were examined for their relationship with plasmid cargo genes. TA loci from the RES-Xre family were highly correlated with virulence plasmids of hypervirulent . Overexpression of the RES toxin KnaT, encoded by the virulence plasmid-carrying RES-Xre locus halts the cell growth of and , whereas co-expression of the cognate Xre antitoxin KnaA neutralizes the toxicity of KnaT. and were co-transcribed, representing the characteristics of a type II TA module. The deletion mutation gradually lost its virulence plasmid in whereas the stability of the plasmid in was enhanced by adding , which revealed that the operon maintained the genetic stability of the large virulence plasmid in . String tests and mouse lethality assays subsequently confirmed that a loss of the virulence plasmid resulted in reduced pathogenicity of . These findings provide important insights into the role of the RES-Xre TA pair in stabilizing virulence plasmids and disseminating virulence genes in e.