Identification of New Delhi metallo-β-lactamase 1 in Acinetobacter lwoffii of food animal origin.

Abstract

BackgroundTo investigate the presence of metallo-β-lactamase (MBL) genes and the genetic environment of the New Delhi metallo-β-lactamase gene bla NDM-1 in bacteria of food animal origin.Methodology/Principal FindingsGram-negative bacteria with low susceptibility to imipenem (MIC>8 µg/mL) were isolated from swab samples collected from 15 animal farms and one slaughterhouse in eastern China. These bacteria were selected for phenotypic and molecular detection of known MBL genes and antimicrobial susceptibility testing. For the bla NDM-1 positive isolate, conjugation and transformation experiments were carried out to assess plasmid transfer. Southern blotting was conducted to localize the bla NDM-1 genes, and DNA sequencing was performed to determine the sequences of bla NDM-1 and the flanking genes. In total, nine Gram-negative bacteria of four different species presented a MBL phenotype. bla NDM-1 was identified on a mobile plasmid named pAL-01 in an Acinetobacter lwoffii isolate of chicken origin. Transfer of pAL-01 from this isolate to E. coli J53 and JM109 resulted in resistance to multiple β-lactams. Sequence analysis revealed that the bla NDM-1 gene is attached to an intact insertion element ISAba125, whose right inverted repeat (IR-R) overlaps with the promoter sequence of bla NDM-1. Thus, insertion of ISAba125 likely enhances the expression of bla NDM-1.ConclusionThe identification of a bla NDM-1- carrying strain of A. lwoffii in chickens suggests the potential for zoonotic transmission of bla NDM-1 and has important implications for food safety.