Carbapenemase-producing Gram-negative bacilli have been a global concern over the past 2 decades because these organisms can cause severe infections with high mortality rates. Carbapenemase genes are often carried by mobile genetic elements, and resistance plasmids can be transferred through conjugation. We conducted whole-genome sequencing (WGS) to demonstrate that the same plasmid harboring a metallo-beta-lactamase gene was detected in two different species isolated from a single patient. Metallo-beta-lactamase-producing Achromobacter xylosoxidans (KUN4507), non-metallo-beta-lactamase-producing Klebsiella pneumoniae (KUN4843), and metallo-beta-lactamase-producing K. pneumoniae (KUN5033) were sequentially isolated from a single patient and then analyzed in this study. Antimicrobial susceptibility testing, molecular typing (pulsed-field gel electrophoresis and multilocus sequence typing), and conjugation analyses were performed by conventional methods. Phylogenetic and molecular clock analysis of K. pneumoniae isolates were performed with WGS, and the nucleotide sequences of plasmids detected from these isolates were determined using WGS. Conventional molecular typing revealed that KUN4843 and KUN5033 were identical, whereas the phylogenetic tree analysis revealed a slight difference. These two isolates were separated from the most recent common ancestor 0.74 years before they were isolated. The same resistance plasmid harboring bla(IMP-19) was detected in metallo-beta-lactamase-producing A. xylosoxidans and K. pneumoniae. Although this plasmid was not self-transferable, the conjugation of this plasmid from A. xylosoxidans to non-metallo-beta-lactamase-producing K. pneumoniae was successfully performed. The susceptibility patterns for metallo-beta-lactamase-producing K. pneumoniae and the transconjugant were similar. These findings supported the possibility of the horizontal transfer of plasmid-borne bla(IMP-19) from A. xylosoxidans to K. pneumoniae in a single patient.