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Multidrug-resistant (MDR) Pseudomonas aeruginosa poses a great challenge to clinical treatment. In this study, we characterized a ST768 MDR P. aeruginosa strain, Pa150, that was isolated from a diabetic foot patient. The minimum inhibitory concentration (MIC) assay showed that Pa150 was resistant to almost all kinds of antibiotics, especially aminoglycosides. Whole genome sequencing revealed multiple antibiotic resistant genes on the chromosome and a 437-Kb plasmid (named pTJPa150) that harbors conjugation-related genes. A conjugation assay verified its self-transmissibility. On the pTJPa150 plasmid, we identified a 16S rRNA methylase gene, rmtB, that is flanked by mobile genetic elements (MGEs). The transfer of the pTJPa150 plasmid or the cloning of the rmtB gene into the reference strain, PAO1, significantly increased the bacterial resistance to aminoglycoside antibiotics. To the best of our knowledge, this is the first report of an rmtB-carrying conjugative plasmid isolated from P. aeruginosa, revealing a novel possible transmission mechanism of the rmtB gene.