Illustration of the ultrastructure of a single bacterium of the genus Salmonella. In a procaryotic bacterial cell, the DNA is not organized in a nucleus but is diffuse; here it appears yellow against the green background of the cytoplasm. Enclosing the cytoplasm is the cell membrane (violet) and the complex cell wall (brown). Toxicity in Salmonella infections is due to endotoxins associated with the outer cell wall. Whip-like flagella project from the inner membrane & shorter pili are rooted in the outer cell wall. The pili facilitate contact with host cells. A polysaccharide capsule (green) forms an outer, protective layer.