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The current study is conducted to detect the pathogenicity of E. coli O157: H7 and know the effects of its experimental infection in the histological structure of the liver of male mice aged (8-12) weeks. In addition, it attempts to determine the therapeutic effect of an approved drug in the treatment of bacteria and compare it with the antibiotic whose effectiveness is tested in vitro. The antibiotic sensitivity test results show that the bacteria are sensitive to Trimethoprim-Sulfamethoxazole, Metronidazole, Gentamicin, Amikacin, Tetracycline, Azithromycin, Ceftriaxone and Ciprofloxacin, and resistant to Amoxicillin/clavulanic acid and Ampicillin. The most sensitive antibiotic is Ciprofloxacin, followed by Trimethoprim-Sulfamethoxazole. Since the latter is an approved and widely used antibiotic, it is chosen with Ciprofloxacin to determine its therapeutic effect against the bacteria under study. Animals experimentally infected with this bacteria show different degrees of clinical signs represented by lethargy, recluse, loss of appetite, increase in respiratory rate and heart beat rate with different degrees of diarrhea appearing in a number of them. In others, different forms of paralysis appear, either paralysis of the hind feet or complete immobilityy, in addition to the occurrence of a number of deaths in mice infected experimentally with the infectious dose of bacteria. As for the results of the histological examination, they are represented in hypertrophy and sometimes hyperplasia in the hepatocytes, loss of chromatin of the nuclei in a number of them with expansion of blood sinusoids, congestion of blood vessels as well as hemorrhage and inflammatory cellular infiltration. These symptoms are more severe in the half lethal dose group (LD-50). As for the groups treated with the two aforementioned antibiotics, it is noted that they play an effective role in stopping diarrhea with mice somewhat regaining their activity. However, they still had suffered from various tissue lesions represented by necrosis, vacuolation, degeneration, inflammatory cellular infiltration, congestion and hemorrhage.