Abstract
Two novel New Delhi metallo-β-lactamase-1 (NDM-1)-positive plasmids containing a complete composite transposon, Tn125, from two respective Acinetobacter towneri isolates were characterized. Plasmid pNDM-GJ01 (30,293 bp) isolated from A. towneri G165 did not show homology to any known plasmid structure, except for the transposon Tn125 containing blaNDM-1. A novel repB gene and two XRE-type transcriptional regulators were found in pNDM-GJ01. Plasmid pNDM-GJ02 (62,011 bp) isolated from A. towneri G295 showed the highest homology to pBJAB0715 (41% coverage, 99% nucleotide identity). In addition to the blaNDM-1-harbouring transposon Tn125, pNDM-GJ02 also had an IS26-composite transposon, which contains ISCR1 and two class 1 integrons carrying different cassette arrays. Both clinical isolates were highly resistant to β-lactams and susceptible to tigecycline and colistin. Ten other resistance genes were detected in G295, and one other resistance gene was detected in G165. No transconjugant was obtained from any of the donors by broth and filter mating. The emergence of these two novel plasmids carrying NDM-1 in Acinetobacter spp., pNDM-GJ01 and pNDM-GJ02, suggests Tn125 mobile integration.
Highlights
The emergence of the blaNDM-1 gene, which confers gram-negative bacteria with antibiotic resistance, has gained worldwide attention owing to its recent and rapid spread[1,2,3]
The two clinical strains showed similar susceptibility profiles: they were resistant to broad-spectrum cephalosporins, carbapenems, fluoroquinolones, and sulfamethoxazole. They showed a slight difference in susceptibility to aminoglycosides: G165 was resistant to amikacin, and was intermediate to gentamicin and tobramycin; G295 was resistant to amikacin and tobramycin, and was intermediate to gentamicin
PNDM-GJ01 and pNDM-GJ02, containing New Delhi metallo-β-lactamase-1 (NDM-1) were found from two A. towneri isolates in China
Summary
The emergence of the blaNDM-1 gene, which confers gram-negative bacteria with antibiotic resistance, has gained worldwide attention owing to its recent and rapid spread[1,2,3]. In 2011, Hu et al reported a blaNDM-1-bearing plasmid, pNDM-BJ01 (GenBank: JQ001791), isolated from a clinical A. lwoffii strain in China[7] This plasmid carried a complete Tn125 transposon and showed high horizontal transfer ability[7]. We report the complete sequences of two novel plasmids, pNDM-GJ01 and pNDM-GJ02, isolated from clinical Acinetobacter towneri strains that do not share any similar structure with pNDM-BJ01 except for Tn125 harbouring the blaNDM-1 gene. Both plasmids were characterized and their complete sequences were elucidated
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