Definition: A genus of motile aerobic bacteria (order Spirochaetales) containing thin, tightly coiled organisms 6–20 mcm in length. They possess an axial filament, and one or both ends may be bent into a semicircular hook. They stain with difficulty except with Giemsa stain or silver impregnation. Associated with icterohemorrhagic fever. They include seven pathogens and three nonpathogenic species; the type species is Leptospira interrogans.
[lepto- + G. speira, a coil]