Characteristics and blaNDM-1 genetic environment of plasmid from Enterobacter aerogenes / 中国感染控制杂志

Objective To study plasmid-mediated transfer,plasmid replicon typing,and genetic environment of blaNDM-1 gene in Enterobacteraerogenes(E.aerogenes).Methods E.aerogenes HN-NDM0711 was used as the subject of this research,the transferable properties of plasmid were analyzed by conjugation testing,conjugant was performed stability testing,plasmid type was determined by PCR-based replicon typing (PBRT),downstream and upstream of blaNDM-1 were sequenced using chromosome walking method,genetic context was analyzed by BLASTN and BALSTP,as well as annotated using Vector NTI 11.5.1 software,sequence pipeline graph was made,the sequence was submitted to Genbank through software Banklt.Results The conjugation testing of E.aerogenes pHN-NDM0711 was positive,after positive conjugant was conducted 4-day passage,minimal inhibitory concentrations (MICs) of imipenem and meropenem to all the cloned strains didn't change,blaNDM-1 were all positive.The replicon type was IncA/C;blaNDM-1 gene was localized between ISAba14 and IS91,at upstream of the blaNDM-1,class 1 integron and Tn3 transposon were identified,class 1 integron contained a new mosaic structure of a drug-resistant resistance gene cassette.Conclusion E.aerogenes pHN-NDM071 1,bearing blaNDM-1 gene in IncA/C plasmid,derived from gene recombination under different antimicrobial selection pressure.Antimicrobial use in clinical,industrial and agricultural area should be strictly controlled,so as to reduce the emergence of such bacteria.

Profiling of antimicrobial resistance and plasmid replicon types in beta-lactamase producing Escherichia coli isolated from Korean beef cattle

In this study, 78 isolates of Escherichia coli isolated from Korean beef cattle farms were investigated for the production of extended-spectrum beta-lactamase (ESBL) and/or AmpC beta-lactamase. In the disc diffusion test with ampicillin, amoxicillin, cephalothin, ceftiofur, cefotaxime, ceftazidime, and cefoxitin, 38.5% of the isolates showed resistance to all of ampicillin, amoxicillin, and cephalothin. The double disc synergy method revealed that none of the isolates produced ESBL or AmpC beta-lactamases. DNA sequencing showed that all isolates encoded genes for TEM-1-type beta-lactamase. Moreover, 78.2% of the isolates transferred the TEM-1-type beta-lactamase gene via conjugation. In plasmid replicon typing of all donors, IncFIB and IncFIA were identified in 71.4% and 41.0% of plasmids, respectively. In transconjugants, IncFIB and IncFIA were the most frequent types detected (61.5% and 41.0%, respectively). Overall, the present study indicates that selection pressures of antimicrobials on beta-lactamases in beef cattle may be low relative to other livestock animals in Korea. Moreover, to reduce selection pressure and dissemination of beta-lactamase, the long-term surveillance of antimicrobial use in domestic beef cattle should be established.