Salmonella Typhi. LM of the Gram-negative, rod-shaped bacteria Salmonella typhi, causative agent of typhoid fever in humans. Typhoid is an infection of the digestive system leading to high fever, chills, rash, & in serious cases inflammation of the spleen and bones and erosion of the intestinal walls. The bacteria are transmitted through food or drinking water contaminated by the feces or urine of patients or carriers. Other species within the Salmonella group are responsible for food poisoning. Magnification: x500 at 35mm size.