Leptospira spirochaetes under scanning electron microscope

Spirochaetes (or Spirochetes) are the phylum Spirochaetae. These are double-membrane bacteria with long, helically coiled (spiral-shaped) cells.

Spirochaetes are bacteria. They have flagella, which run lengthwise between the cell wall and outer membrane. The flagella cause a twisting motion which moves the spirochaete about.

Most spirochaetes are free-living and anaerobic, but there are many parasitic species.