This animation shows how pathogenic E. coli bacteria bind to intestinal cells.

Although most Escherichia coli (E. coli) bacteria are harmless, certain pathogenic strains can infect the human intestinal tract, causing severe diarrhea and even death. The animation illustrates how a pathogenic E. coli bacterium uses a series of proteins to attach itself to a human intestinal epithelial cell.

As shown, the bacterium latches onto the host cell using long protein filaments known as pili. The bacterium then uses a syringe-like mechanism, called the Type III secretion system, to inject bacterial proteins into the cell. Some of these proteins become receptors in the host cell’s membrane, which help the bacterium bind firmly to the cell’s surface. The proteins also trigger a pathway that causes the host cell to form a “pedestal” for the bacterium. As more and more bacteria bind to the intestinal lining, diarrhea and other symptoms of the infection begin.

This animation is a clip from a 1999 Holiday Lecture Series, 2000 and Beyond: Confronting the Microbe Menace. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different features or steps in the process.