Pathology MCQ3

Pathology MCQ3:

A 60-year-old man has had persistent bloody diarrhea, abdominal cramps, and fever for thepast week. On physical examination,his temperature is 38.1° C. He has mild diffuse 

abdominal pain. A stool sample is positive for occult blood. Colonoscopy shows marked mucosal erythema with focal ulceration from the rectum to the ascending colon. The ulcers do not penetrate the muscularis propria. A biopsy is performed, and the microscopic appearance of the specimen is shown in 

the figure. Which of the following infectious organisms is most likely to produce these findings?

A Bacillus cereus

B Entamoeba histolytica   

C Giardia lamblia

D Salmonella enterica

E Shigella flexneri

F Vibrio cholerae

Explanation:

Amebiasis is a common cause of dysentery in developing nations. The figure shows few single-cell protozoa invading tissue with inflammatory cells(Inset:Entamoeba with ingested RBCs). Entamoeba histolytica organisms are resistant to gastric acid and can 

invade the colonic submucosa via contact-dependent cytolysis. The amebae not only produce local necrosis with ulceration and hemorrhage, but also gain access to the ve-

nules of the portal system, which drains to the liver. Amebic liver abscess is an uncommon complication of amebiasis.

The colonic lesions typically have disappeared by the time the liver lesions appear. In some cases, there can be extensive mucosal involvement with characteristic flask-shaped (similar to an Erlenmeyer flask) ulcerations similar to those seen in other severe inflammatory bowel diseases.

 Bacillus cereus is a cause of food poisoning (most often as a contaminant in reheated fried rice) and has a short incubation time. Giardiasis tends to involve the small intestine 

and produces variable inflammation, but no ulceration. 

Salmonellosis more typically involves the small intestine and in most cases produces self-limited enteritis, although more severe disease with dissemination to other organs can occur with Salmonella typhi infection. 

Shigellosis can produce bloody dysentery with irregular superficial colonic mucosal ulceration, but the organisms typically do 

not invade beyond the lamina propria. 

Cholera is characterized by massive, secretory diarrhea without intestinal mucosal invasion or necrosis.

So the correct option is B( Entamoeba histolytica).