Two novel bla NDM-1 -harbouring transposons on pPrY2001-like plasmids coexisting with a novel cfr-encoding plasmid in food animal source Enterobacteriaceae.

Objectives: This study reports identification of the carbapenemase-encoding gene from carbapenem-resistant Enterobacterales from food animals.
Methods: A total of 40 bacterial isolates recovered from 475 faecal swabs obtained on one farm were tested for the presence of the bla _NDM-1 gene by PCR. Species identification of three bla _NDM-1 -positive strains was conducted by MALDI-TOF/MS. Antimicrobial susceptibility testing was performed by broth microdilution. Transferability of the bla _NDM-1 and cfr genes was determined by filter mating. The genetic environment of bla _NDM-1 and cfr was analysed by whole-genome sequencing.
Results: Two Proteus mirabilis (JPM24 and YPM35) and one Providencia rettgeri (YPR25) carried bla _NDM-1 . The bla _NDM-1 genes were located on conjugable pPrY2001-like plasmids often reported to carry important antimicrobial resistance genes (ARGs). YPR25 and YPM35 shared two almost identical conjugable plasmids, one carrying bla _NDM-1 and the other cfr. The bla _NDM-1 gene in YPR25 (same as YPM35) and JPM24 was located in two novel transposons, designated Tn6922 and Tn6923, respectively. Tn6922 and Tn6923 carried 14 and 7 ARGs, respectively, and both contained multiple copies of IS26 in the same direction, with a high degree of similarity. Additionally, cfr was located on a plasmid with an unreported high frequency of conjugative transfer in YPR25 (same as YPM35).
Conclusion: We identified two novel bla _NDM-1 -containing transposons (Tn6922 and Tn6923) present on pPrY2001-like plasmids. The pPrY2001-like bla _NDM-1 plasmids coexisted with a novel cfr plasmid, and both could transfer at high frequency, highlighting the importance of continuous surveillance of multiresistant Enterobacterales of animal origin that can serve as a reservoir for ARGs.
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