Prevalence of fosfomycin resistance among CTX-M-producing Escherichia coli clinical isolates in Japan and identification of novel plasmid-mediated fosfomycin-modifying enzymes.

We evaluated the in vitro activity of fosfomycin against a total of 192 CTX-M beta-lactamase-producing Escherichia coli strains isolated in 70 Japanese clinical settings. Most of the isolates (96.4%) were found to be susceptible to fosfomycin. On the other hand, some of the resistant isolates were confirmed to harbor the novel transferable fosfomycin resistance determinants named FosA3 and FosC2, which efficaciously inactivate fosfomycin through glutathione S-transferase activity.