Purpose: Several subtypes of plasmid-mediated fosfomycin resistance gene fosA  in Enterobacteriaceae have been reported worldwide and have caused concern. The present study characterized a novel member of fosA  gene located on a plasmid from Escherichia coli .
Materials and Methods: A fosfomycin-resistant E. coli  isolate PK9 was recovered from a chicken meat sample in 2018. The presence of fosA  genes was detected by PCR and sequencing. Whole-genome sequencing (WGS), conjugation, and cloning were performed to identify the mechanism responsible for fosfomycin resistance. Oxford Nanopore MinION sequencing was carried out to characterize the plasmid carrying fosfomycin resistance gene and the genetic context of the novel fosA  variant.
Results: A novel fosA  gene with significant homology (> 98%) with fosA6  and fosA5  genes was identified by WGS and was named fosA10 . FosA10 shared 56.1% to 98.6% amino acid sequence identity with other reported plasmid-mediated FosA enzymes. Fosfomycin resistance and fosA10  gene were successfully transferred to E. coli  C600 by conjugation. Cloning confirmed that FosA10 could confer fosfomycin resistance (MIC > 128 μg/mL). The fosA10  gene was localized on a 53kb IncFII (F35:A-:B-) plasmid. The ∆lysR-fosA10-∆hp  fragment (4328 bp), located between two copies of IS10R, showed 100% identity with the chromosomal sequences of 17 Klebsiella pneumoniae  strains of ST664 and one of ST3821 in GenBank.
Conclusion: Our findings indicated that the fosA10  gene of E. coli  might be captured from the chromosome of K. pneumoniae  by IS 10 , which further demonstrated that K. pneumoniae  might act as a reservoir of fosA -like genes acquired by E. coli .
Keywords: fosfomycin, resistance, plasmid, animal products