Coloured scanning electron micrograph (SEM) of spirochaetes. Spirochaetes are a group comprised of six genera of bacteria in a family known as Spirochaete. They are named because of their spiral shape. Typically, spirochaetes are very slender. Their length can vary from about five microns to several hundred microns, depending on the species. Spirochaeta are free-living nonpathogenic inhabitants of mud and water, typically thriving in anaerobic (oxygen-deprived) environments. Other species of spirochaetes however are a significant health threat to humans. Both syphilis and Lyme disease are caused by spirochetes. Beneficially, spirochetes contribute to digestion in ruminants such as cows. Magnification: x7000 when printed at 10 centimetres wide.