Shigella sonnei is an rod-shaped, gram-negative bacteria. It is a foodborne pathogen that causes the food poisoning "shigellosis." The bacterium is spread by the ingestion of food or water contaminated by infected feces. Symptoms include diarrhea, blood in stool, mucus in stool, pus in stool, and fever. Children and the elderly are more affected by infection. Rehydration and antibiotics are used for treatment. Magnification: 500x.