Clustered Gram-negative Salmonella Typhimurium bacteria are shown under a magnification of 5000X in a colorized scanning photomicrograph. (AP Photo/Centers for Disease Control and Prevention, Janice Haney Carr) ** FILE **

Photo by: Janice Haney Carr

Clustered Gram-negative Salmonella Typhimurium bacteria are shown under a magnification of 5000X in a colorized scanning photomicrograph. (AP Photo/Centers for Disease Control and Prevention, Janice Haney Carr) ** FILE **