Effect of antimicrobial agents, especially fosfomycin, on the production and release of Vero toxin by enterohaemorrhagic Escherichia coli O157:H7.

In 1996, Japan had several large outbreaks of enterohaemorrhagic Escherichia coli (EHEC) O157:H7 infection. We surveyed physicians who examined and treated these patients, and found that most of the patients (95.9%) received antimicrobial agents as treatments, in particular, fosfomycin comprised 84.0% of the prescribed treatment. Since the administration of antimicrobial agents for EHEC infection is under discussion, we also analyzed the effects of 7 antimicrobial agents including fosfomycin on the production and release of Vero toxins (VTs) by EHEC. The addition of fosfomycin into EHEC culture in CAYE broth at 5 h after the start of incubation caused a marked increase of VT1 release and production, as revealed by an immunological toxin assay (RPLA). However, a cytotoxicity assay of Vero cells showed a small increase of biological activity in the specimens treated with fosfomycin because the Vero cell assay reflects total cytotoxicity of VT1 and VT2. These results indicate that further study is necessary before concluding whether antimicrobial agents actually worsen an EHEC infection.