Two carbapenem-resistant avian Escherichia coli strains ST10 and ST354 mediated by blaNDM-5 gene

Abstract:

[Background] Carbapenem-resistant Enterobacteriaceae is now becoming a globally serious threat to public health. [Objective] To study the carbapenem resistance of intestinal bacteria isolated from poultry farms, feces of chicken and duck were screened at Xi’an of Shaanxi and Haining of Zhejiang Provinces. [Methods] The potential bacterial colonies on LB agar plate containing meropenem were picked and further characterized by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). Minimum inhibitory concentration (MIC) was determined by the microbroth dilution method. Whole genome sequencing was performed by the Illumina HiSeq platform. Acquired resistance genes were predicted by the online ResFinder database analysis. In addition, plasmids and carbapenem resistance genes were confirmed by S1-pulsed-field gel electrophoresis (S1-PFGE) and Southern blot hybridization. [Results] Two carbapenem-resistant Escherichia coli strains HN1-26 and XN3-1 were isolated. Both of these strains were resistant to ceftazidime, ceftiofur, ampicillin, amoxicillin/clavulanate, trimethoprim/sulfamethoxazole, sulfisoxazole, enrofloxacin, ofloxacin, meropenem and tetracycline. Besides, XN3-1 was also shown to be resistant to florfenicol and spectinomycin. Multilocus sequence typing (MLST) results revealed that HN1-26 and XN3-1 were ST354 and ST10, respectively. The MIC values of these two strains to meropenem were 64 μg/mL, while HN1-26 grew faster than XN3-1 on LB plate with meropenem. Furthermore, these two strains contained the identical IncX3 type plasmid carrying antibiotic resistance gene blaNDM-5, with a size of 46 161 bp. This IncX3 type plasmid contained complete conjugative elements and were able to transfer to E. coli recipient cells. [Conclusion] Our results suggested that the IncX3 plasmid is an important vehicle for transferring blaNDM-5 gene, which has the risk of spreading in livestock and poultry in China.