To investigate the presence of metallo-β-lactamase (MBL) genes and the genetic environment of the New Delhi metallo-β-lactamase gene blaNDM-1 in bacteria of food animal origin.
Gram-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 blaNDM-1 positive isolate, conjugation and transformation experiments were carried out to assess plasmid transfer. Southern blotting was conducted to localize the blaNDM-1 genes, and DNA sequencing was performed to determine the sequences of blaNDM-1 and the flanking genes. In total, nine Gram-negative bacteria of four different species presented a MBL phenotype. blaNDM-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 blaNDM-1 gene is attached to an intact insertion element ISAba125, whose right inverted repeat (IR-R) overlaps with the promoter sequence of blaNDM-1. Thus, insertion of ISAba125 likely enhances the expression of blaNDM-1.
The identification of a blaNDM-1- carrying strain of A. lwoffii in chickens suggests the potential for zoonotic transmission of blaNDM-1 and has important implications for food safety.
Available at: http://works.bepress.com/qijing-zhang/17/