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The emergence of carbapenem-hydrolysing metallo-β-lactamases (MBLs) is a serious threat to the clinical utility of carbapenems. This study identified plasmid- and integron-borne bla IMP-1 and bla IMP-10 in clinical isolates of Serratia marcescens. The bla IMP-1 and bla IMP-10 gene cassettes were carried by a class 1 integron and followed by the aac(6′)-IIc gene cassette. The bla IMP-1 and bla IMP-10 gene cassettes were preceded by a weak Pant promoter, TGGACA(N)17TAAGCT, and an inactive P2 promoter, TTGTTA(N)14TACAGT. These genes were easily transferred to Escherichia coli by conjugation and transformation, indicating that they are located on transferable plasmids. Due to the acquisition of bla IMP-1, the susceptibility of E. coli transconjugants to imipenem, meropenem, panipenem and biapenem decreased by 32-, 256-, 64- and 128-fold, respectively. In comparison, after gaining bla IMP-10, the susceptibility of E. coli transconjugants to the four carbapenems decreased by 64-, 2048-, 256- and 64-fold, respectively. Strains harbouring bla IMP-10 showed higher-level resistance to imipenem, meropenem and panipenem than the strains harbouring bla IMP-1, although the nucleotide sequences of the class 1 integrons carrying bla IMP-10 and bla IMP-1 were identical except for a single point mutation.