At left, an image from the National Institute of Allergy and Infectious Diseases shows a clump of Staphylococcus epidermidis bacteria (green) in the extracellular matrix, which connects cells and tissue, taken with a scanning electron microscope. At right, an image provided by the U.S. Department of Agriculture shows the bacterium Enterococcus faecalis, which lives in the human gut, just one type of microbe being studied in the Human Microbiome Project. Associated Press