Efficacy of Antibiotic Therapy for Infection with Shiga-Like Toxin-Producing Escherichia coli O157 : H7 in Mice with Protein-Calorie Malnutrition

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Abstract
Antibiotic therapy for infection with Shiga-toxin-producing Escherichia coli O157 : H7 is controversial because of the possibility of its inducing hemolytic uremic syndrome and acute encephalopathy. In a previous study, mice with protein-calorie malnutrition were found to be highly susceptible to this pathogen. The efficacy of oral antibiotic therapy in malnourished mice infected with O157 organisms was assessed. Mice fed a low-protein calorie diet were infected intragastrically with 2×106 colony-forming units of a Shiga-toxin-producing strain of Escherichia coli O157 : H7. Infected mice were orally given a therapeutic dose of an antibiotic, including norfloxacin, fosfomycin, kanamycin, ampicillin, clarithromycin or trimethoprim-sulfamethoxazole for 3 days: mice on protocol A received the antibiotic on days 1–3, starting on the day after infection, and mice on protocol B received the antibiotic on days 3–5. The duration of fecal pathogen excretion was shorter and the toxin level in the stool and blood lower in the mice that received protocol A than in untreated mice; all of the mice treated on protocol A survived the lethal infection. All antibiotics except trimethoprim-sulfamethoxazole, administered on protocol B, exhibited the same effect as that exhibited by the respective antibiotic administered on protocol A. Only the mice treated with protocol B of trimethoprim-sulfamethoxazole had a higher toxin level in the blood than untreated controls, resulting in 95% mortality. These results suggest that the antibiotics used in this study, except for trimethoprim-sulfamethoxazole, could reduce the risk of hemolytic uremic syndrome and acute encephalopathy following Escherichia coli O157 : H7 infection in humans, and that fosfomycin, in particular, may be relevant for testing in humans.

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