Integration of the blaNDM-1 carbapenemase gene into a novel SXT/R391 integrative and conjugative element in Proteus vulgaris

Objectives: To characterize the genetic environment of the carbapenem resistance determinant in Proteus vulgaris of swine origin. Methods: The carbapenem-resistant P. vulgaris strain BC22 was isolated from a faecal swab from a diseased pig with diarrhoea in Sichuan Province of China in 2018. The presence of carbapenemase genes was screened by PCR. WGS and bioinformatics analysis were performed to analyse the genetic environment of the carbapenem resistance determinant. Results: P. vulgaris strain BC22 was found to harbour the carbapenemase gene bla(NDM-1). WGS data revealed that bla(NDM-1) was located in a truncated ISAba125 composite transposon. The carbapenem resistance gene bla(NDM-1) and 20 other resistance genes, including the multiresistance gene cfr and the bifunctional aminoglycoside/quinolone resistance gene aac(6')-lb-cr, were located in a novel SXT/R391 integrative and conjugative element (ICE). This new SXT/R391 ICE of 148.7 kb was chromosomally located, and could be transferred to Escherichia coli. Conclusions: Here, we report a carbapenemase gene, blaNDM-1, integrated into an SXT/R391 ICE. Our study highlights that this SXT/R391 ICE may facilitate the dissemination of clinically important resistance genes such as bla(NDM-1), cfr and aac(6')-lb-cr.