Which statement best describes Shigella in terms of virulence and clinical presentation?

• A. Nonpathogenic to humans
• B. Immotile and causes bloody diarrhea
• C. Causes watery diarrhea
• D. Produces heat-stable toxin

Answer: (B)

Shigella stands out for its ability to invade the lining of the colon, especially the M cells over Peyer’s patches, and trigger a strong inflammatory response that damages the mucosa. This invasion leads to dysentery—bloody, often mucoid stools with crampy abdominal pain and fever. The organism is inherently nonmotile, which helps distinguish it from motile enteric pathogens like Salmonella. While some Shigella strains can produce Shiga toxin, the hallmark clinical picture—bloody diarrhea from mucosal invasion—fits best with this nonmotile, invasive pattern. In contrast, truly watery diarrhea is more typical of secretory toxins from pathogens like ETEC or Cholera, and nonpathogenic organisms or those producing a heat-stable toxin don’t describe Shigella’s invasive, inflammatory syndrome.