Urinary tract infections (UTI) are common worldwide and are becoming increasingly\ndifficult to treat because of the development of antibiotic resistance. Immunocompetent murine\nmodels of human UTI have been used to study pathogenesis and treatment but not for investigating\nresistance development after treatment with antibiotics. In this study, intravesical inoculation of\nuropathogenic Escherichia coli CFT073 in immunocompetent Balb/c mice was used as a model of human\nUTI. The value of the model in investigating antibiotic exposure on in vivo emergence of antibiotic\nresistance was examined. Experimentally infected mice were treated with 20 or 200 mg/kg ampicillin,\n5 or 50 mg/kg ciprofloxacin, or 100 or 1000 mg/kg of fosfomycin. Ampicillin and ciprofloxacin\nwere given twice daily at 8 h intervals, and fosfomycin was given once daily. Antibiotic treatment\nbegan 24 h after bacterial inoculation and ended after 72 h following the initial treatment. Although\nminimum inhibitory concentrations (MIC) for the experimental strain of E. coli were exceeded at\npeak concentrations in tissues and consistently in urine, low levels of bacteria persisted in tissues in\nall experiments. E. coli from bladder tissue, kidney, and urine grew on plates containing 1* MIC of\nantibiotic, but none grew at 3 *MIC. This model is not suitable for studying emergent resistance but\nmight serve to examine bacterial persistence.
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