In vitro bactericidal activity of antimicrobial agents against enterohaemorrhagic Escherichia coli

Abstract

Objectives: In vitro bactericidal activity of four antimicrobial agents was determined against nine strains of enterohaemorrhagic Escherichia coli. Methods: Pulsed-field gel electrophoresis was carried out with the Bio-Rad Gene Path system. Each antimicrobial agent was added to logarithmic phase of enterohaemorrhagic E. coli (four strains of E. coli O157:H7, two of E. coll O26, two of E. coli O111, and one of E. coli O165) in broth to obtain a concentration of 10 or 50 mg/L, and viable cells were counted after 1, 2, 6 and 24 h. Results: All nine strains were confirmed to differ in their DNA pattern by pulsed-field gel electrophoresis. Norfloxacin at concentrations of 10 and 50 mg/L had bactericidal effects on all nine strains of enterohaemorrhagic E. coli. However, cefoperazone, kanamycin and fosfomycin had no bactericidal effects on some strains. In particular, after addition of 10 mg/L fosfomycin or kanamycin, four of the nine strains showed proliferation. Conclusions: Norfloxacin had marked bactericidal effects on enterohaemorrhagic E. coli. This information could be of value in planning randomized clinical trials of antimicrobial agents as treatment for enterohaemorrhagic E. coli infection. © The British Society for Antimicrobial Chemotherapy 2004; all rights reserved.