SEM of Leptospira bacteria. Leptospira is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species.Leptospira was first observed in 1907 in kidney tissue slices of a leptospirosis victim who was described as having died of "yellow fever." Leptospira have a gram-negative cell envelope consisting of a cytoplasmic and outer membrane. Leptospira, both pathogenic and saprophytic, can occupy diverse environments, habitats and life cycles; these bacteria are found throughout the world, except in Antarctica.