Plasmids Harboring a Tandem Duplicate of blaVIM-24 in Carbapenem-Resistant ST1816 Pseudomonas aeruginosa in Japan

The aim of this study was to clarify the biological and clinical significance of a tandem duplicate of blaVIM-24 in Pseudomonas aeruginosa ST1816 isolates. Thirteen ST1816 isolates carrying a plasmid harboring blaVIMs were obtained from two medical settings in Japan between 2016 and 2019. Complete sequencing revealed that, of the 13 plasmids, four had a tandem duplicate of blaVIM-24. These four plasmids harbored a replicon, a relaxase gene, and T4SS genes belonging to IncP-9, MOBF, and MPFT, respectively. All four plasmids transferred to PAO1 by filter mating. Cefepime marginally affected the growth of PAO1, carrying a pUCP19 harboring the tandem duplicate. Western blotting analysis showed that the relative intensity of VIM-24 metallo-β-lactamase produced by a PAO1 transformant containing a tandem duplicate was 2.6-fold higher than that produced by a PAO1 transformant containing a single copy. These results suggest that the tandem duplicate of blaVIM-24 in plasmids may confer resistance against cefepime, enabling P. aeruginosa ST1816 strains to proliferate in hospitals in Japan.