Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights reserved.): Electron micrograph of Leptospira biflexa (color added). Leptospira spp. are spirochetes possessing a helical cell body ranging in length from about 10 to 20 μm with a diameter of 0.15 μm. (See related articles on pages 3249 and 3255.)