Final answer:
Treponema pallidum causes syphilis, which is identified through specific serological testing and microscopic techniques since it's difficult to culture in a laboratory setting.
Step-by-step explanation:
The motile spirochete Treponema pallidum is responsible for the sexually transmitted infection known as syphilis. This bacterium is part of a larger group of spirochetes, some of which are human pathogens causing a variety of diseases, with syphilis being notably prevalent.
Treponema pallidum is a gram-negative spirochete that lacks lipopolysaccharide endotoxin typical of other gram-negative bacteria, but it does contain lipoproteins which can induce an immune response in the host.
Detection and diagnosis of syphilis involve serological testing and microscopic techniques, like using a darkfield microscope to observe live, unstained spirochetes, given that this bacterium cannot be cultured in the laboratory on artificial media.