Infection, Detection, Protection     Meet the Microbes
Still counting: 4,000 species have been identified, but there are probably millions more. Picture of Vibrio cholerae, Salmonella and Intestinal Bacteria
Spirals, squiggles and more: Bacteria come in lots of shapes, including balls, rods, commas, spirals, and cubes. On the go: Some swim forward by beating a tail called a flagellum; others slide on the slimy secretions they ooze.