Search

To investigate the prevalence of a tet (A) gene variant and its role in developing high-level tigecycline resistance among carbapenem-resistant Klebsiella pneumoniae (CRKP) clinical isolates. The mechanism of high-level tigecycline resistance in CRKP mediated by a tet (A) variant was explored by induction experiments, antimicrobial susceptibility testing, whole-genome sequencing and bioinformatics analysis. The amplification and overexpression of the tet (A) variant were measured by the determination of sequencing depth, gene copy numbers, and qRT-PCR. A high rate (62.1%, 998/1607) of tet (A) variant carriage was observed among 1607 CRKP clinical isolates from Henan Province, China. High-level tigecycline resistance could rapidly develop by the amplification of the tet (A) variant in these isolates. The analysis of the raw sequencing data and the plasmid mapping depth revealed that the Δ tnpA homologous sequence of Tn 1721 supports the amplification of the region that harbours the tet (A) variant by forming a large number of repeat arrays through translocatable units (TUs). Moreover, the epidemiological analysis of tet (A) variant-carrying structures among 1607 clinical CRKPs showed that the TU structure is widely present. The presence of a tigecycline resistance-mediating tet (A) variant in CRKP clinical isolates represents a greater health concern than initially thought and should be monitored consistently. [ABSTRACT FROM AUTHOR]

Objectives: To identify the genetic context and the transferability of the multiresistance gene lsa(E) in Listeria monocytogenes.Methods: MICs were determined by broth microdilution. Transferability of lsa(E) was investigated by conjugation, electrotransformation and natural transformation. The lsa(E)-carrying plasmid was sequenced using the Illumina MiSeq and PacBio RSII platforms. The presence of translocatable units (TUs) was examined by PCR.Results: The 85 555 bp non-conjugative multiresistance plasmid pNH1 from L. monocytogenes harboured nine antimicrobial resistance genes including a multiresistance gene cluster, consisting of the genes aphA3, erm(B), aadE, spw, lsa(E) and lnu(B), and in addition the genes dfrG, tet(S) and catA8 were also located on plasmid pNH1 The multiresistance gene cluster, and each of the genes tet(S), catA8 and cadA were flanked by IS1216 elements. PCR identified four types of TUs, consisting of either the multiresistance gene cluster and one copy of IS1216, the catA8 gene and one copy of IS1216, or both, but also the tet(S) gene and one copy of IS1216, respectively. Natural transformation into Streptococcus mutans UA159 yielded transformants that harboured a novel 13 208 bp transposon, designated Tn6659. This transposon consisted of the multiresistance gene cluster bounded by IS1216 copies. All transformants displayed elevated MICs of the respective antimicrobial agents. At the integration site in the transformants, 8 bp direct target duplications (5'-ATTCAAAC-3') were found immediately up- and downstream of Tn6659.Conclusions: To the best of our knowledge, this is the first report of this novel multiresistance gene cluster and the gene catA8, flanked by IS1216 elements located on a plasmid of L. monocytogenes. Moreover, a novel functionally active multiresistance transposon was identified. [ABSTRACT FROM AUTHOR]