High Rate of MCR-1-Producing Escherichia coli and Klebsiella pneumoniae among Pigs, Portugal

Abstract

The mcr-1 (mobile colistin resistance 1) gene, which encodes phosphoethanolamine transferase, has been recently identified as a source of acquired resistance to polymyxins in Escherichia coli. Using the SuperPolymyxin selective medium, we prospectively screened 100 pigs at 2 farms in Portugal for polymyxin-resistant Enterobacteriaceae and recovered 98 plasmid-mediated MCR-1-producing isolates. Most isolates corresponded to nonclonally related E. coli belonging to many sequence types; we also found 2 Klebsiella pneumoniae sequence types. The mcr-1 gene was carried on IncHI2 or IncP plasmid backbones. Our finding of a high rate of MCR-1 producers on 2 pig farms in Portugal highlights the diffusion of that colistin-resistance determinant at the farm level. The fact that the pigs received colistin as metaphylaxis in their feed during the 6 weeks before sampling suggests selective pressure.

Keywords: Escherichia coli; Klebsiella pneumonia; MCR-1; Portugal; antimicrobial resistance; bacteria; colistin; mcr-1 gene; pigs.

Figure

Genetic environments associated with the mcr-1 (mobile colistin resistance 1) gene detected in select Enterobacteriacae isolates from pigs, Portugal, by PCR. I) 1 copy of ISApl1 associated with mcr-1 in 5′ region; II) 2 copies of ISApl1 in 5′ and 3′ regions of mcr-1; III) no copy of ISApl1 associated with mcr-1; IV) truncated copy of ISApl1 associated with mcr-1 in 5′ region inserted in a kinase gene. IS, insertion sequence; orf, open reading frame.