Bacillary dysentery is most commonly caused by which organism?

• A. Escherichia coli
• B. Shigella dysenteriae
• C. Salmonella typhi
• D. Vibrio cholerae

Answer: (B)

Bacillary dysentery is an inflammatory diarrhea where the bacteria invade the lining of the colon, causing bloody, mucus-filled stools and crampy abdominal pain. The classic culprit is Shigella dysenteriae, a highly infectious organism that penetrates the colonic mucosa (often via M cells) and triggers intense inflammation and ulceration. Some strains also produce Shiga toxin, which can worsen tissue injury. Transmission is typically fecal-oral, often occurring in crowded or unsanitary settings. Other organisms listed cause different illnesses—Salmonella typhi leads to typhoid fever, Vibrio cholerae causes profuse watery diarrhea without blood, and certain E. coli strains cause other forms of diarrheal disease—so Shigella dysenteriae best fits the description of bacillary dysentery.