Salmonella typhimurium is a rod-shaped, gram-negative bacterium that causes gastroenteritis (salmonellosis) in humans. Symptoms include diarrhea, fever, vomiting, and abdominal cramps. Usually salmonellosis is not fatal, but it can lead to severe dehydration. S. typhimurium is one of the most common types of Salmonella in the United States. The bacteria can be spread through contaminated meat, eggs or dairy products; tainted fruits and vegetables; rodents; and the skin of certain reptiles. Magnification: 1000x. Brightfield