Abstract
E. coli O157:H7 are an important pathogen of human and animals. The puppies were divided into
two groups randomly, infected group: (15 puppies) were drenched once orally with 5 ml bacterial
suspension of PBS containing 5×107 CFU, and control group: (5 puppies) drenched 5 ml PBS, then
specimens from internal organs including: kidney, intestine, liver, spleen, brain and lung after sacrificed
puppies at (24hrs, 48hrs, 72hrs, 6 days, 12days, 24days, and 36days) from infected and control groups
were used for histopathological examination. After inoculation, all animals were examined for presence or
absence of signs. The shedding patterns of E. coli O157:H7 in feces were started after 24hrs. after
inoculation and ceased at day 14th.The results of gross lesions of internal organs revealed no gross lesions
in the intestine, kidney, lung and spleen at 24, 48 and 72 hours. While at days 6, 12, 24, 36 the intestine
showed congestion and hemorrhage. Also the kidneys were swollen and showed congestion. The lung
showed sever hemorrhages at day 12 post infection, also the spleen showed enlargement at day 24 post
infection. The results of histopathological changes showed that E. coli O157:H7 infection caused
thrombus development, necrosis, vacuolar degeneration of epithelial lining cells and congestion of blood
vessels of kidney and intestine with superficial sloughing of epithelial mucosa of intestine at 24hrs and
48hrs. post-infection at 48hrs post-infection. Also the result revealed infiltration of inflammatory cells,
vacuolar degeneration appeared in the examined organs at 72hrs. At 6-day post infection the infiltration of
inflammatory cells became more prominent with severe congestion of blood vessels in examined organs.
At day 12 post infection, there was mucus attachment in the epithelium of intestine, congestion of blood
vessels, necrosis, with infiltration of the inflammatory cells in the examined organs. The most important
event at day 24 post infection is the presence of regeneration in the intestine which became more prominent
at day 36 post infection. This study aimed to highlighting the gross and histopathological effect of E. coli
O157:H7 in different organs post inoculation in puppies. In conclusion, the shiga toxin can cause damage
in many body organs like liver, spleen, kidney, lung, brain and intestine.

Key words: E. coli, histopathology, puppies, inflammatory cells.