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

The New Delhi metallo-beta-lactamase-1 (NDM-1) gene, bla (NDM-1), is an emerging plasmid-borne drug resistance gene, which encodes for exceptionally broad-spectrum beta-lactamase, being able to hydrolyze a wide variety of beta-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 5 nm 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.