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Carbapenemase-producing Klebsiella pneumoniae (CP-Kp) is a real global health threat. Environmental reservoirs of resistance gene determinats, such as effluents of hospital wastewaters, are acquiring increased relevance in the selection of plasmid-encoded carbapenemase genes. The presence of Hg in environmental reservoirs may exert a positive selective pressure on tolerant bacteria, favoring the co-transfer of carbapenemase genes and mer operons. In our study, 63 CP-Kp isolates were screened for mer operons by whole genome sequencing (MySeq). Conjugation assays were performed with 24 out of 63 CP-Kp isolates harboring the mer operon. Ten transconjugants (Tc-Kp) were selected with Hg. Plasmid DNA of Tc-Kp was extracted and sequenced using single-molecule real-time (SMRT) technology (PacBio, Sequel II system) with later annotation. Plasmid analysis revealed that Tc-Kp from blaIMP-like (n = 3) showed a single plasmid belonging to IncC group with two complete mer operon next to blaIMP-like. Tc-Kp from blaVIM-1 (n = 2) harbored two plasmids, one with blaVIM-1 in an IncL, and mer operon was in an IncFIB plasmid. Tc-Kp from blaOXA-48-like (n = 5) showed 2 plasmids. blaOXA-48-like was found in an IncL plasmid, whereas mer operon was (i) in an IncR plasmid associated with blaCTX-M-15 in 3 Tc-Kp-OXA-48-like, (ii) in an IncC plasmid associated with blaCMY-2 in 1 Tc-Kp-OXA-48-like, (iii) and in an IncFIB plasmid associated with blaCTX-M-15 in 1 Tc-Kp-OXA-48-like. This is, to our knowledge, the first study to describe in K. pneumoniae producing plasmid-encoded carbapenemase, the potential impact of Hg in the co-transfer of mer operons and carbapenemase genes located in the same or different plasmids. Key points: • Environmental reservoirs are playing an important role in the selection of carbapenemase genes. • Conjugation assays, selecting with Hg, obtained 10 transconjugants with carbapenemase genes. • mer operons were located in the same or different plasmids than carbapenemase genes. [ABSTRACT FROM AUTHOR]