Spirochaetes (also spelled spirochetes) belong to a phylum of distinctive diderm (double-membrane) bacteria, most of which have long, helically coiled (spiral-shaped) cells. Spirochaetes are chemoheterotrophic in nature, with lengths between 5 and 250 µm and diameters around 0.1–0.6 µm. Spirochaetes are distinguished from other bacterial phyla by the location of their flagella, sometimes called axial filaments, which run lengthwise between the bacterial inner membrane and outer membrane in periplasmic space. These cause a twisting motion which allows the spirochaete to move about. When reproducing, a spirochaete will undergo asexual transverse binary fission. Most spirochaetes are free-living and anaerobic, but there are numerous exceptions. Treponemes readily attach to endothelial cells and pass through blood vessel walls; facilitates dissemination; can also pass through placenta.Nonpathogenic treponemes do not attach. Some of the histopathology associated with syphilitic lesions results from activation of host defenses. Antibodies, in association with complement or macrophages and T lymphocytes that interact with organisms, may indirectly damage the host tissues. T. pallidum elaborates a protein that facilitate the spread of the organisms by hematogenous dissemination. The organisms coat themselves with host serum protein. May initially protect them from immune system. No vaccine yet despite intense research in this area. Treatment: Penicillin used for treatment of all stages of disease. Check for Brucellosis