Treponema pallidum is a type of bacterium that is responsible for causing syphilis, a sexually transmitted infection. It is a spiral-shaped organism that is difficult to see under a standard microscope, requiring special techniques for identification. The bacterium can enter the body through mucous membranes or broken skin, often during sexual contact. Once inside the body, Treponema pallidum can spread through the bloodstream, leading to various stages of syphilis, including primary, secondary, latent, and tertiary stages. Each stage has distinct symptoms, ranging from sores to rashes and, if untreated, can result in serious health complications affecting the heart, brain, and other organs.