SALMONELLA INFANTIS. SALMONELLA INFANTIS This scanning electron micrograph (SEM) depicts a number of highly magnified rod-shaped, motile, Gram-negative Salmonella infantis bacteria, some of which are attached, Magnification 18875x. Salmonellosis is an infection due to members of a genus of bacteria called Salmonella, of which S. infantis is a member. Most persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4