Abstract: Objective To investigate the effect of pathway and dose of inoculation on establish-ment of experimental tuberculosis in SD rats.Methods Eighty male SD rats were randomized into eight groups.The rats in group C,group D and group E were injected intravenously with 0.1 mg, 1 mg,10mg of Mycobacterium tuberculosis standard strain H37Rv,respectively.The rats of group F,group G and group H were injected intraperitoneally with 0.1mg,1mg,10mg of Mycobacterium tuberculosis standard strain H37Rv,respectively.The rats of group A and group B were injected in- travenously and intraperitoneally with the normal saline,respectively.All rats were sacrificed at six weeks postinfection.Their lungs,livers,and spleens were observed pathologic changes,weighed to compare weight index of organs.The lung,liver,spleen homogenates were cultured for mycobacte- rial growth,smeared and stained to find acid-fast bacilli.Results The histopathological changes in the lungs,livers and spleens showed that macrophages and epithelioid cells aggregated within the tubercle lesion whose periphery are surrounded by lymphocytes.With increasement of dose of inoc- ulation,tubercle lesion change and positive rate of mycobacterial culture of lung,liver and spleen tissues from experimental groups were increasing.Lung,liver,spleen sections with Ziehl-Neelsen staining showed that red,small and short acid-fast bacilli arrayed disorderly within macrophages and inflammatory tubercle.Tubercle lesion change and positive rate of mycobacterial culture of lung,liver,spleen in rats from the groups infected by caudal vein were higher than that from the groups infected by abdominal cavity with the same doses of inoculation.Conclusions Caudal vein pathway is better than abdominal cavity pathway in establishing experimental tuberculosis in SD rat.SD rats can be infected by Mycobacterium tuberculosis and can be used as animal model of ex- perimental tuberculosis.

Key words: Sprague-Dawley rats, Tuberculosis, Mycobacterium tuberculosis/microbiology Animal model