Introduction: The occurrence and development of antibiotic resistance are mainly caused by the spread of large plasmids carrying multiple antibiotic resistance genes. Recently, the association between 16S rRNA methyltransferase genes and β-lactamase genes carried by the same plasmid is of concern.
Methods: The Klebsiella aerogenes  1564 was isolated from the catheter tip of a patient in a tertiary hospital, Shanghai, China. The presence of the bla _NDM-1 and rmtC  genes were assessed by PCR. Complete sequence of plasmid p1564 was determined. The K. aerogenes  1564 was characterized by antimicrobial susceptibility testing, Carbapenemase phenotype confirmation testing, conjugation experiment, S1-PFGE and multilocus sequence typing (MLST).
Results: Herein, we found that a New Delhi Metallo-β-lactamase-1 gene (bla _NDM-1) and a 16S rRNA methyltransferase gene (rmtC ) coexisted on a transferrable plasmid of a carbapenem-resistant K. aerogenes  clinical isolate. The K. aerogenes  clinical isolate was found to belong to a novel sequence type 192 (ST192) determined by MLST. The sequencing results of the plasmid p1564 carrying bla _NDM-1 gene and rmtC  gene showed that the size and guanine-cytosine content of the plasmid were 136, 902 bp and 51.8%, with 164 putative ORFs and two multidrug resistance gene islands. In addition to bla _NDM-1 and rmtC , the plasmid contained bleomycin resistance gene (ble _MBL), CMY-6β-lactamase gene (bla _CMY-6), quaternary ammonium compound resistance gene (sugE ), truncated quaternary ammonium compound resistance gene (qacEΔ1 ), aminoglycoside resistance gene (aacA4 ) and sulfonamide resistance gene (sul1 ). By comparison, p1564 has high homology with pHS36-NDM from Salmonella enterica  subsp. enterica  serovar Stanley reported in China, with similar size and both belonging to plasmid incompatibility group A/C.
Conclusion: The present study demonstrated for the first time the co-existence of rmtC  and bla _NDM-1 in a novel ST192 K. aerogenes . The spread of plasmids harboring both bla _NDM-1 and rmtC  may occur among Enterobacteriaceae in China.
Keywords: Klebsiella aerogenes , plasmid, bla _NDM-1, rmtC