Emergence of NDM-1-positive capsulated Escherichia coli with high resistance to serum killing in Japan

Abstract

The New Delhi metallo-β-lactamase-1 (NDM-1) gene, bla (NDM-1), is an emerging plasmid-borne drug resistance gene, which encodes for exceptionally broad-spectrum β-lactamase, being able to hydrolyze a wide variety of β-lactams, including carbapenems, and was first reported in Klebsiella pneumoniae from a Swedish patient of Indian origin in 2009. It is widely distributed among Enterobacteriacae and has geographically exhibited extremely rapid and global spread. In this study, we characterized the bla (NDM-1)-positive ST38 Escherichia coli strain NDM-1 Dok01 (which was isolated from the blood of a 54-year-old Japanese inpatient, who had previously visited India), focusing on bacterial surface structures related to virulence. The E. coli culture contained colony variants, which developed a transparent smooth colony and a rough colony on blood agar plates. The smooth colony-forming cells (substrain M1) possessed a surface capsule and were resistant to serum killing, whereas rough colony-forming mutants (substrain B2) lacked a capsule (and a 5.3-kb plasmid) and were highly susceptible to serum killing. Reflecting the surface structural difference, substrain M1 was more flagellated and motile, whereas substrain B2 was less flagellated and apparently possessed straight pili 5nm wide, which played a role in adherence to human intestinal cells and bacterial autoaggregation. Data suggest that the bla (NDM-1)-positive ST38 E. coli has emerged in Japan and that it is a capsulated bacterial pathogen with virulence potential in the blood stream.