what is treponema pallidum

Treponema pallidum is a bacterium that causes syphilis, a sexually transmitted disease (STD) . It is a motile spirochete that is generally acquired by close sexual contact and can enter the host via breaches in squamous or columnar epithelium. T. pallidum is a fastidious organism that exhibits narrow optimal ranges of pH, Eh, and temperature. It is a helically coiled microorganism usually 6–15 μm long and 0.1–0.2 μm wide. In addition to syphilis, the genus Treponema contains both pathogenic and nonpathogenic species. Human pathogens cause four treponematoses: yaws, endemic syphilis, and pinta. Nonpathogenic treponemes may be part of the normal flora of the intestinal tract, the oral cavity, or the genital tract.