DIRECT EVIDENCE OF NEURON IMPAIRMENT BY ORAL INFECTION WITH VEROTOXIN-PRODUCING ESCHERICHIA-COLI-O157-H- IN MITOMYCIN-TREATED MICE

We developed a mouse model of acute encephalopathy induced by verotoxi n 2 variant (VT2v)-producing Escherichia coli. Three-week-old mice wer e inoculated intragastrically with approximately 10(10) CFU off. coli 0157:H strain E32511/HSC and simultaneously given an intraperitoneal i njection of mitomycin (MMC; 2.5 mg/kg). Drinking water containing 5 g of streptomycin sulfate per liter was given ad libitum from 3 days bef ore the infection. From 1 to 2 days after bacterial inoculation, clini cal features including weight loss, weakness, and flaccid paralysis of the extremities developed, usually culminating in death within 4 days . Diarrhea was not observed during the course of disease. No mice died in the absence of streptomycin or MMC treatment for 2 weeks after the oral bacterial infection. Judging from the clinical course and the bi ochemical and histological examination, the cause of death was not lik ely to be attributable to renal failure or to a side effect of MMC. To better understand the cause of death, we examined the brain cortex an d spinal cord of the moribund mice by electron microscopy. Mice shelvi ng mortal symptoms were given horseradish peroxidase intravenously. Th e tracer was present in the endothelial basal lamina, in the surroundi ng extracellular spaces, and even in the neuron fibers of the brain co rtex. Furthermore, immunoreactivity of VT2v, proved by the use of rabb it anti-VT2 serum, was localized selectively in the damaged myelin she aths of neuron fibers which were accompanied by edematous axons in the brain cortex and spinal cord. These findings strongly suggest that VT 2v is toxic to both endothelial cells and neurons in the central nervo us system and subsequently causes fatal acute encephalopathy.