National Escherichia, Shigella, Vibrio Reference Unit at CDC

Under a high magnification of 10961x, this colorized scanning electron micrograph (SEM) depicted a number of Gram-negative <i>Escherichia coli</i> bacteria of the strain O157:H7. <i>E. coli</i> O157:H7 is one of hundreds of strains of this bacterium. Although most strains are harmless, and live in the intestines of healthy humans and animals, this strain produces a powerful toxin, which can cause severe illness.<p><i>E. coli</i> O157:H7 was first recognized as a cause of illness in 1982 during an outbreak of severe bloody diarrhea; the outbreak was traced to contaminated hamburgers. Since then, most infections have come from eating undercooked ground beef.<p>The combination of letters and numbers in the name of the bacterium refers to the specific markers found on its surface, which distinguishes it from other types of <i>E. coli</i>. See PHIL 8797 for a black and white version of this image.